keyctl.c: make use of RVAL_DECODED

keyctl.c: make use of RVAL_DECODED

* keyctl.c (sys_add_key, sys_request_key): Update for RVAL_DECODED.
(keyctl_join_session_keyring, keyctl_handle_key,
keyctl_set_reqkey_keyring): Remove.
(keyctl_get_keyring_id, keyctl_update_key, keyctl_handle_key_key,
keyctl_read_key, keyctl_keyring_search, keyctl_chown_key,
keyctl_instantiate_key, keyctl_instantiate_key_iov, keyctl_negate_key,
keyctl_reject_key, keyctl_set_timeout, keyctl_get_persistent,
keyctl_setperm_key): Change to return void.
Update for RVAL_DECODED.
(sys_keyctl): Update callers.  Update for RVAL_DECODED.