Added return for non-void return function for arduino support

[chacalnoir]

lf_arduino_support.c has no return in the lf_sleep function with signature: int lf_sleep(interval_t sleep_duration)

If some warnings are treated as errors (which is done by default on a Windows 11 WSL Ubuntu 22.04 installation), the following error prevents compilation:

/xxx/src/core/platform/lf_arduino_support.c: In function 'lf_sleep':
/xxx/src/core/platform/lf_arduino_support.c:99:1: error: control reaches end of non-void function [-Werror=return-type]
   99 | }
      | ^
cc1: some warnings being treated as errors

This PR fixes that issue by adding a return 0, which resolves the compilation issue.

[lhstrh]

Looks good to me! Thanks for the fix 👍