mmc: sdhci-s3c: fix incorrect spinlock usage after merge

In the commit f522886e

 a merge conflict
in the sdhci-s3c driver been fixed. However the fix used incorrect
spinlock operation - it caused a race with sdhci interrupt service. The
correct way to solve it is to use spin_lock_irqsave/irqrestore() calls.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>