Fix error handling for secure element keys in `psa_start_key_creation`

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index bbd6b24..4beda81 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1841,6 +1841,9 @@
 
         status = psa_copy_key_material_into_slot(
             slot, (uint8_t *) (&slot_number), sizeof(slot_number));
+        if (status != PSA_SUCCESS) {
+            return status;
+        }
     }
 
     if (*p_drv == NULL && method == PSA_KEY_CREATION_REGISTER) {