drm/rect: Fix formatting of example code

Drive-by polish.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483044517-5770-9-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_rect.c

@@ -371,7 +371,7 @@ EXPORT_SYMBOL(drm_rect_rotate);
  * to the vertical axis of the original untransformed
  * coordinate space, so that you never have to flip
  * them when doing a rotatation and its inverse.
- * That is, if you do:
+ * That is, if you do ::
  *
  *     drm_rotate(&r, width, height, rotation);
  *     drm_rotate_inv(&r, width, height, rotation);