ARM: EXYNOS: Fix compiler warning in dma.c file

Fixes the following warning:
warning: 'dma_dmamask' defined but not used [-Wunused-variable]
Signed-off-by: NSachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>

arch/arm/mach-exynos/dma.c

@@ -35,8 +35,6 @@
 #include <mach/irqs.h>
 #include <mach/dma.h>
 
-static u64 dma_dmamask = DMA_BIT_MASK(32);
-
 static u8 exynos4210_pdma0_peri[] = {
 	DMACH_PCM0_RX,
 	DMACH_PCM0_TX,