[media] vcodec: mediatek: mark pm functions as __maybe_unused

When CONFIG_PM is disabled, we get a couple of unused functions:

drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c:927:13: error: 'mtk_jpeg_clk_off' defined but not used [-Werror=unused-function]
 static void mtk_jpeg_clk_off(struct mtk_jpeg_dev *jpeg)
             ^~~~~~~~~~~~~~~~
drivers/media/platform/mtk-jpeg/mtk_jpeg_core.c:916:13: error: 'mtk_jpeg_clk_on' defined but not used [-Werror=unused-function]
 static void mtk_jpeg_clk_on(struct mtk_jpeg_dev *jpeg)

Rather than adding more error-prone #ifdefs around those, this patch
removes the existing #ifdef checks and marks the PM functions as __maybe_unused
to let gcc do the right thing.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Rick Chang <rick.chang@mediatek.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>