mmc: dw_mmc: replace spin_lock_irqsave by spin_lock in hard IRQ

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

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1604627813-59785-1-git-send-email-tiantao6@hisilicon.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>