drm/exynos: fix linux framebuffer address setting.

With iommu, buffer->dma_addr has device addres so this patch
fixes for physical address to be set to fix.smem_start always.
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_fbdev.c

@@ -87,7 +87,8 @@ static int exynos_drm_fbdev_update(struct drm_fb_helper *helper,
 
 	dev->mode_config.fb_base = (resource_size_t)buffer->dma_addr;
 	fbi->screen_base = buffer->kvaddr + offset;
-	fbi->fix.smem_start = (unsigned long)(buffer->dma_addr + offset);
+	fbi->fix.smem_start = (unsigned long)(page_to_phys(buffer->pages[0]) +
+				offset);
 	fbi->screen_size = size;
 	fbi->fix.smem_len = size;