net: ethernet: mtk_wed: fix some possible NULL pointer dereferences

Fix possible NULL pointer dereference in mtk_wed_detach routine checking
wo pointer is properly allocated before running mtk_wed_wo_reset() and
mtk_wed_wo_deinit().
Even if it is just a theoretical issue at the moment check wo pointer is
not NULL in mtk_wed_mcu_msg_update.
Moreover, honor mtk_wed_mcu_send_msg return value in mtk_wed_wo_reset()

Fixes: 79968444 ("net: ethernet: mtk_wed: introduce wed wo support")
Fixes: 4c5de09e ("net: ethernet: mtk_wed: add configure wed wo support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>