iio: adc: fsl-imx25-gcq: Use devm_* and dev_err_probe() to simplify probe

Custom callbacks are need for regulators (so there is a handle to read
the voltage from) and the clk because it is retrieved from the parent
rather than directly from firmware description.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240218172731.1023367-3-jic23@kernel.org


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