mmc: mediatek: Avoid ugly error message when SDIO wakeup IRQ isn't used

When I boot a kukui-kodama board, I see an ugly warning in my kernel
log:
  mtk-msdc 11240000.mmc: error -ENXIO: IRQ sdio_wakeup not found

It's pretty normal not to have an "sdio_wakeup" IRQ defined. In fact,
no device trees in mainline seem to have it. Let's use the
platform_get_irq_byname_optional() to avoid the error message.

Fixes: 527f36f5 ("mmc: mediatek: add support for SDIO eint wakup IRQ")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20230510064434.1.I935404c5396e6bf952e99bb7ffb744c6f7fd430b@changeid


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>