ARM: S5P: fix incorrect loop iterator usage on gpio-interrupt

Loop iterator value after terminating list_for_each_entry()
is not NULL. This patch fixes incorrect iterator usage in
GPIO interrupt code for SAMSUNG S5P platforms.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>