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