Put device node in error path in fec_enet_init_stop_mode().

Fixes: 8a448bf8 ("net: ethernet: fec: move GPR register offset and bit into DT")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220426125231.375688-1-yangyingliang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>