ARM: SAMSUNG: Fix compiler warning in dma-ops.c file

Fixes the following build warning:
arch/arm/plat-samsung/dma-ops.c:129:2: warning: initialization from incompatible pointer type [enabled by default]
arch/arm/plat-samsung/dma-ops.c:129:2: warning: (near initialization for 'dmadev_ops.release') [enabled by default]

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>