drm/udl: introduce a macro to convert dev to udl.

This just makes it easier to later embed drm into udl.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190405031715.5959-3-airlied@gmail.com
diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
index f8ff5a6..16593d4 100644
--- a/drivers/gpu/drm/udl/udl_fb.c
+++ b/drivers/gpu/drm/udl/udl_fb.c
@@ -82,7 +82,7 @@ int udl_handle_damage(struct udl_framebuffer *fb, int x, int y,
 		      int width, int height)
 {
 	struct drm_device *dev = fb->base.dev;
-	struct udl_device *udl = dev->dev_private;
+	struct udl_device *udl = to_udl(dev);
 	int i, ret;
 	char *cmd;
 	cycles_t start_cycles, end_cycles;
@@ -210,7 +210,7 @@ static int udl_fb_open(struct fb_info *info, int user)
 {
 	struct udl_fbdev *ufbdev = info->par;
 	struct drm_device *dev = ufbdev->ufb.base.dev;
-	struct udl_device *udl = dev->dev_private;
+	struct udl_device *udl = to_udl(dev);
 
 	/* If the USB device is gone, we don't accept new opens */
 	if (drm_dev_is_unplugged(udl->ddev))
@@ -437,7 +437,7 @@ static void udl_fbdev_destroy(struct drm_device *dev,
 
 int udl_fbdev_init(struct drm_device *dev)
 {
-	struct udl_device *udl = dev->dev_private;
+	struct udl_device *udl = to_udl(dev);
 	int bpp_sel = fb_bpp;
 	struct udl_fbdev *ufbdev;
 	int ret;
@@ -476,7 +476,7 @@ int udl_fbdev_init(struct drm_device *dev)
 
 void udl_fbdev_cleanup(struct drm_device *dev)
 {
-	struct udl_device *udl = dev->dev_private;
+	struct udl_device *udl = to_udl(dev);
 	if (!udl->fbdev)
 		return;
 
@@ -487,7 +487,7 @@ void udl_fbdev_cleanup(struct drm_device *dev)
 
 void udl_fbdev_unplug(struct drm_device *dev)
 {
-	struct udl_device *udl = dev->dev_private;
+	struct udl_device *udl = to_udl(dev);
 	struct udl_fbdev *ufbdev;
 	if (!udl->fbdev)
 		return;