iio: multiplexer: Switch to use dev_err_probe() helper

iio: multiplexer: Switch to use dev_err_probe() helper

In the probe path, dev_err() can be replaced with dev_err_probe()
which will check if error code is -EPROBE_DEFER and prints the
error name. It also sets the defer probe reason which can be
checked later through debugfs. It's more simple in error path.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220927064841.319291-1-yangyingliang@huawei.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>