mctp: check register_netdevice_notifier() error in mctp_device_init()

mctp: check register_netdevice_notifier() error in mctp_device_init()

mctp_device_init() handles errors from rtnl_af_register() and
rtnl_register_many(), but ignores the return value of
register_netdevice_notifier(). If notifier registration fails, init can
still return success while the module is only partially initialized.

Check the notifier registration error and fail module init early.

Fixes: 583be982d934 ("mctp: Add device handling and netlink interface")
Signed-off-by: Minhong He <heminhong@kylinos.cn>
Link: https://patch.msgid.link/20260720072518.112614-1-heminhong@kylinos.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>