drm: Remove set but not used variable 'config'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/drm_plane.c: In function 'drm_mode_getplane_res':
drivers/gpu/drm/drm_plane.c:475:26: warning:
 variable 'config' set but not used [-Wunused-but-set-variable]
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1536646814-186429-1-git-send-email-yuehaibing@huawei.com

drivers/gpu/drm/drm_plane.c

@@ -472,7 +472,6 @@ int drm_mode_getplane_res(struct drm_device *dev, void *data,
 			  struct drm_file *file_priv)
 {
 	struct drm_mode_get_plane_res *plane_resp = data;
-	struct drm_mode_config *config;
 	struct drm_plane *plane;
 	uint32_t __user *plane_ptr;
 	int count = 0;
@@ -480,7 +479,6 @@ int drm_mode_getplane_res(struct drm_device *dev, void *data,
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;
 
-	config = &dev->mode_config;
 	plane_ptr = u64_to_user_ptr(plane_resp->plane_id_ptr);
 
 	/*