secvar/backend: fix comment of get_hash_to_verify
get_hash_to_verify claims to return a negative error code in the
case of error. It actually returns NULL. Fix the comment.
@@ -610,7 +610,7 @@ err_pkcs7:
* Create the hash of the buffer
* name || vendor guid || attributes || timestamp || newcontent
* which is submitted as signed by the user.
- * Returns the sha256 hash, else negative error code.
+ * Returns the sha256 hash, else NULL.
*/
static char *get_hash_to_verify(const char *key, const char *new_data,
const size_t new_data_size,
