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 <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_buf.c

@@ -63,7 +63,8 @@ static int lowlevel_buffer_allocate(struct drm_device *dev,
 			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) {