iio: adc: at91_adc: Simplify with dev_err_probe()

Use the dev_err_probe() helper to simplify error handling during probe.
This also handle scenario, when EDEFER is returned and useless error
is printed.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/20230828064546.2383857-4-ruanjinjie@huawei.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>