iio: imu: adis16480: Improve getting the optional clocks

iio: imu: adis16480: Improve getting the optional clocks

The extended clocks are optional and may not be present for some
configurations supported by this driver. Nevertheless, in case
the clock is provided but some error happens during its getting,
that error handling should be done properly.

Use devm_clk_get_optional() API and report possible errors using
dev_err_probe() to handle properly -EPROBE_DEFER error.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Tested-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220414131559.24694-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>