error: parameter 'output_size' set but not used

[maflcko]

This happens on clang-14 with -Wunused-but-set-parameter set.

The affected code:

https://github.com/ARMmbed/mbedtls/blob/78e84e860d8430fe57ac606e357309d92b144f44/library/psa_crypto_cipher.c#L267

This breaks the mbedtls project in oss-fuzz.

[gilles-peskine-arm]

Note that we generally don't support development versions of compilers, so normally we'd ignore warnings issued by Clang 14 until it's officially released. We're making an exception here because oss-fuzz uses development versions of Clang and we want it to build.