Fix build errors with MBEDTLS_PSA_CRYPTO_STORAGE_C disabled
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index efec00b..e035ece 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1307,6 +1307,7 @@
 static psa_status_t psa_finish_key_creation( psa_key_slot_t *slot )
 {
     psa_status_t status = PSA_SUCCESS;
+    (void) slot;
 
 #if defined(MBEDTLS_PSA_CRYPTO_STORAGE_C)
     if( slot->lifetime == PSA_KEY_LIFETIME_PERSISTENT )