iio: adc: rzg2l_adc: Switch to RUNTIME_PM_OPS() and pm_ptr()

iio: adc: rzg2l_adc: Switch to RUNTIME_PM_OPS() and pm_ptr()

The use of SET_RUNTIME_PM_OPS() is now deprecated and requires
__maybe_unused annotations to avoid warnings about unused functions.
Switching to RUNTIME_PM_OPS() and pm_ptr() eliminates the need for such
annotations because the compiler can directly reference the runtime PM
functions, thereby suppressing the warnings. As a result, the
__maybe_unused markings can be removed.

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/20241206111337.726244-6-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>