drm: Move a dereference below a NULL test

If the NULL test is necessary, then the dereference should be moved below
the NULL test.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
type T;
expression E;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
  ... when != E
      when != i
  if (E == NULL) S
+ i = E->fld;
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/gpu/drm/drm_stub.c

@@ -489,7 +489,7 @@ int drm_put_minor(struct drm_minor **minor_p)
  */
 void drm_put_dev(struct drm_device *dev)
 {
-	struct drm_driver *driver = dev->driver;
+	struct drm_driver *driver;
 	struct drm_map_list *r_list, *list_temp;
 
 	DRM_DEBUG("\n");
@@ -498,6 +498,7 @@ void drm_put_dev(struct drm_device *dev)
 		DRM_ERROR("cleanup called no dev\n");
 		return;
 	}
+	driver = dev->driver;
 
 	drm_vblank_cleanup(dev);