mmc: sdhci-s3c: fix NULL ptr access in sdhci_s3c_remove

If not all clocks have been defined in platform data, the driver will
cause a null pointer dereference when it is removed. This patch fixes
this issue.

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