Add guards for mbedtls_psa_crypto_free()

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

programs/pkey/key_app_writer.c

@@ -409,7 +409,9 @@ exit:
     mbedtls_mpi_free(&DQ); mbedtls_mpi_free(&QP);
 
     mbedtls_pk_free(&key);
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
     mbedtls_psa_crypto_free();
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(_WIN32)
     mbedtls_printf("  + Press Enter to exit this program.\n");