drm/exynos: Fix address space warning in exynos_drm_buf.c

Fixes the following warning:
drivers/gpu/drm/exynos/exynos_drm_buf.c:66:29: warning:
incorrect type in assignment (different address spaces)
drivers/gpu/drm/exynos/exynos_drm_buf.c:66:29:
expected void [noderef] <asn:2>*kvaddr
drivers/gpu/drm/exynos/exynos_drm_buf.c:66:29: got void *

Signed-off-by: Sachin Kamat <[e-mail]>
Signed-off-by: Inki Dae <[e-mail]>

drivers/gpu/drm/exynos/exynos_drm_buf.c

···
 			return -ENOMEM;
 		}
 
-		buf->kvaddr = dma_alloc_attrs(dev->dev, buf->size,
+		buf->kvaddr = (void __iomem *)dma_alloc_attrs(dev->dev,
+					buf->size,
 					&buf->dma_addr, GFP_KERNEL,
 					&buf->dma_attrs);
 		if (!buf->kvaddr) {