media: marvell-ccic: Fix -Wunused-function warnings

If CONFIG_PM is n, gcc warns:

drivers/media/platform/marvell-ccic/mmp-driver.c:324:12: warning: ‘mmpcam_runtime_suspend’ defined but not used [-Wunused-function]
 static int mmpcam_runtime_suspend(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~
drivers/media/platform/marvell-ccic/mmp-driver.c:310:12: warning: ‘mmpcam_runtime_resume’ defined but not used [-Wunused-function]
 static int mmpcam_runtime_resume(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~

Mark them as __maybe_unused to fix this.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>