iio: adc: rcar-gyroadc: Use pm_runtime_resume_and_get() and check in probe()

1 instance found using coccicheck script under review at:
https://lore.kernel.org/lkml/20210427141946.2478411-1-Julia.Lawall@inria.fr/


The other instance changed did not check for failure of the
pm_runtime_get_sync() so that is added.

Note the remaining pm_runtime_get_sync() call is left alone because it
is not obvious what to do on failure to power up in remove()

This is a prequel to taking a closer look at the runtime pm in IIO drivers
in general.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Marek Vasut <marek.vasut@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210509113354.660190-29-jic23@kernel.org