mmc: mxcmmc: replace spin_lock_irqsave with spin_lock in ISR

As you are already in ISR, it is unnecessary to call spin_lock_irqsave.

Signed-off-by: jun qian <hangdianqj@163.com>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>