iio: adc: imx7d_adc: Switch to DEFINE_SIMPLE_DEV_PM_OPS() and pm_sleep_ptr()

In this case we only gain the ability to have the compiler drop the
struct dev_pm_ops because the callbacks are called from paths other
than suspend and resume.  In general the purpose of this new macro
is to allow automated removal of the callbacks as well, but that doesn't
apply here.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20220621202719.13644-5-jic23@kernel.org