KEYS: remove unnecessary get/put of explicit dest_keyring

In request_key_and_link(), in the case where the dest_keyring was
explicitly specified, there is no need to get another reference to
dest_keyring before calling key_link(), then drop it afterwards.  This
is because by definition, we already have a reference to dest_keyring.

This change is useful because we'll be making
construct_get_dest_keyring() able to return an error code, and we don't
want to have to handle that error here for no reason.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>

security/keys/request_key.c

@@ -546,9 +546,7 @@ struct key *request_key_and_link(struct key_type *type,
 	if (!IS_ERR(key_ref)) {
 		key = key_ref_to_ptr(key_ref);
 		if (dest_keyring) {
-			construct_get_dest_keyring(&dest_keyring);
 			ret = key_link(dest_keyring, key);
-			key_put(dest_keyring);
 			if (ret < 0) {
 				key_put(key);
 				key = ERR_PTR(ret);