mmc: mediatek: Replace spin_lock_irqsave by spin_lock in hard IRQ

The code has been in a irq-disabled context since it is hard IRQ. Therefore
there no need to do it again.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1603068193-44688-1-git-send-email-tiantao6@hisilicon.com


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