make: make list-ttys broken for iotlab-m3

[miri64]

Description

When using

make list-ttys

the serial for an iotlab-m3 is not shown properly anymore. For 2020.10 it still works. According to my bisect any RIOT version after cb66089 is affected.

With samr21-xpro I can still read the serial.

Steps to reproduce the issue

make -C examples/hello-world list-ttys

Expected results

make: Entering directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/hello-world'
/sys/bus/usb/devices/1-2.4: IoT-LAB M3, serial: '<serial if configured>', tty(s): ttyUSB0, ttyUSB1
/sys/bus/usb/devices/1-2.3: IoT-LAB M3, serial: '<serial if configured>', tty(s): ttyUSB2, ttyUSB3
make: Leaving directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/hello-world'

Actual results

make: Entering directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/hello-world'
find: ‘/sys/bus/usb/devices/1-2.4/1-2.4:1.0/ttyUSB0/tty\n/sys/bus/usb/devices/1-2.4/1-2.4:1.1/ttyUSB1/tty’: No such file or directory
find: ‘/sys/bus/usb/devices/1-2.3/1-2.3:1.0/ttyUSB2/tty\n/sys/bus/usb/devices/1-2.3/1-2.3:1.1/ttyUSB3/tty’: No such file or directory
make: Leaving directory '/home/mlenders/Repositories/RIOT-OS/RIOT/examples/hello-world'

Versions

Any RIOT version after cb66089.

Operating System Environment
----------------------------
         Operating System: "Arch Linux" 
                   Kernel: Linux 5.11.5-arch1-1 x86_64 unknown
             System shell: GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu)
             make's shell: GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu)

Installed compiler toolchains
-----------------------------
               native gcc: gcc (GCC) 10.2.0
        arm-none-eabi-gcc: arm-none-eabi-gcc (Arch Repository) 10.2.0
                  avr-gcc: avr-gcc (GCC) 10.2.0
         mips-mti-elf-gcc: missing
           msp430-elf-gcc: missing
       riscv-none-elf-gcc: missing
  riscv64-unknown-elf-gcc: missing
     riscv-none-embed-gcc: missing
     xtensa-esp32-elf-gcc: missing
   xtensa-esp8266-elf-gcc: missing
                    clang: clang version 11.1.0

Installed compiler libs
-----------------------
     arm-none-eabi-newlib: "4.1.0"
      mips-mti-elf-newlib: missing
        msp430-elf-newlib: missing
    riscv-none-elf-newlib: missing
riscv64-unknown-elf-newlib: missing
  riscv-none-embed-newlib: missing
  xtensa-esp32-elf-newlib: missing
xtensa-esp8266-elf-newlib: missing
                 avr-libc: "2.0.0" ("20150208")

Installed development tools
---------------------------
                   ccache: ccache version 4.2
                    cmake: cmake version 3.19.6
                 cppcheck: Cppcheck 2.3
                  doxygen: 1.9.1
                      git: git version 2.30.2
                     make: GNU Make 4.3
                  openocd: Open On-Chip Debugger 0.10.0+dev-01089-g3bfe49266 (2020-02-26-14:18)
                   python: Python 3.9.2
                  python2: Python 2.7.18
                  python3: Python 3.9.2
                   flake8: 3.8.4 (mccabe: 0.6.1, pycodestyle: 2.6.0, pyflakes: 2.2.0) CPython 3.9.2 on
               coccinelle: spatch version 1.0.8 compiled with OCaml version 4.11.1

[miri64]

Duplicate of #15814