ARM: SAMSUNG: fix watchdog reset issue with clk_get()

clkdev framework uses global mutex to protect clock tree, so it is not
possible to call clk_get() in interrupt context. This patch fixes this
issue and makes system reset by watchdog call working again.

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>