Clarify psa_destroy_key documentation

Co-authored-by: Janos Follath <[email protected]>
Signed-off-by: Ryan Everett <[email protected]>

library/psa_crypto.c

@@ -1118,7 +1118,7 @@ psa_status_t psa_destroy_key(mbedtls_svc_key_id_t key)
 
 #if defined(MBEDTLS_PSA_CRYPTO_STORAGE_C)
     if (!PSA_KEY_LIFETIME_IS_VOLATILE(slot->attr.lifetime)) {
-        /* Destroy the copy of the persistent key from memory.
+        /* Destroy the copy of the persistent key from storage.
          * The slot will still hold a copy of the key until the last reader
          * unregisters. */
         status = psa_destroy_persistent_key(slot->attr.id);