mmc: mediatek: mark PM functions as __maybe_unused

The #ifdef check for the suspend/resume functions is wrong:

drivers/mmc/host/mtk-sd.c:2765:12: error: unused function 'msdc_suspend' [-Werror,-Wunused-function]
static int msdc_suspend(struct device *dev)
drivers/mmc/host/mtk-sd.c:2779:12: error: unused function 'msdc_resume' [-Werror,-Wunused-function]
static int msdc_resume(struct device *dev)

Remove the #ifdef and mark all four as __maybe_unused to aovid the
problem.

Fixes: c0a2074a

 ("mmc: mediatek: Fix system suspend/resume support for CQHCI")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20201203222922.1067522-1-arnd@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>