drm/exynos: Make g2d_userptr_get_dma_addr static

Fixes the following warning:
drivers/gpu/drm/exynos/exynos_drm_g2d.c:327:12: warning:
symbol 'g2d_userptr_get_dma_addr' was not declared. Should it be static?

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

drivers/gpu/drm/exynos/exynos_drm_g2d.c

@@ -324,7 +324,7 @@ out:
 	g2d_userptr = NULL;
 }
 
-dma_addr_t *g2d_userptr_get_dma_addr(struct drm_device *drm_dev,
+static dma_addr_t *g2d_userptr_get_dma_addr(struct drm_device *drm_dev,
 					unsigned long userptr,
 					unsigned long size,
 					struct drm_file *filp,