net: mdio: mux-mmioreg: Switch to use dev_err_probe() helper

dev_err() can be replace with dev_err_probe() which will check if error
code is -EPROBE_DEFER.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220915065043.665138-2-yangyingliang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>