iio: adc: rzg2l_adc: Simplify the runtime PM code

iio: adc: rzg2l_adc: Simplify the runtime PM code

All Renesas SoCs using the rzg2l_adc driver manage ADC clocks through PM
domains. Calling pm_runtime_{resume_and_get, put_sync}() implicitly sets
the state of the clocks. As a result, the code in the rzg2l_adc driver that
explicitly manages ADC clocks can be removed, leading to simpler and
cleaner implementation.

Additionally, replace the use of rzg2l_adc_set_power() with direct PM
runtime API calls to further simplify and clean up the code.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/20241206111337.726244-5-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>