media: omap3isp: fix warning for !CONFIG_PM

The final version of the COMPILE_TEST patch for this driver missed
one warning about suspend/resume functions that can now appear
on platforms that don't always set CONFIG_PM:

drivers/media/platform/omap3isp/isp.c:1008:13: error: 'isp_resume_modules' defined but not used [-Werror=unused-function]
 static void isp_resume_modules(struct isp_device *isp)
             ^~~~~~~~~~~~~~~~~~
drivers/media/platform/omap3isp/isp.c:974:12: error: 'isp_suspend_modules' defined but not used [-Werror=unused-function]
 static int isp_suspend_modules(struct isp_device *isp)

This marks the respective functions as __maybe_unused as an easy
workaround.

Fixes: 24313113 ("media: omap3isp: Allow it to build with COMPILE_TEST")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>