media: ov2685: mark PM functions as __maybe_unused

Without CONFIG_PM, we get a harmless build warning:

drivers/media/i2c/ov2685.c:516:12: error: 'ov2685_runtime_suspend' defined but not used [-Werror=unused-function]
 static int ov2685_runtime_suspend(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~
drivers/media/i2c/ov2685.c:507:12: error: 'ov2685_runtime_resume' defined but not used [-Werror=unused-function]
 static int ov2685_runtime_resume(struct device *dev)

This marks the affected functions as __maybe_unused.

Fixes: e3861d91 ("media: ov2685: add support for OV2685 sensor")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[hans.verkuil@cisco.com: fixed typo in Subject: was ov5695]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>