psa_aead_check_nonce_length: Fix unused variable warining

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>

library/psa_crypto.c

@@ -3592,6 +3592,7 @@ static psa_status_t psa_aead_check_nonce_length( psa_algorithm_t alg,
             break;
 #endif /* PSA_WANT_ALG_CHACHA20_POLY1305 */
         default:
+            (void) nonce_length;
             return( PSA_ERROR_NOT_SUPPORTED );
     }