drm: trivial documentation fix to drm_for_each_connector_iter

While reading drm_for_each_connector_iter, I noticed a mention to
drm_connector_begin which doesn't exist. It should be
drm_connector_get.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170421003819.17685-1-krisman@collabora.co.uk

include/drm/drm_connector.h

@@ -1052,7 +1052,7 @@ void drm_connector_list_iter_end(struct drm_connector_list_iter *iter);
  *
  * Note that @connector is only valid within the list body, if you want to use
  * @connector after calling drm_connector_list_iter_end() then you need to grab
- * your own reference first using drm_connector_begin().
+ * your own reference first using drm_connector_get().
  */
 #define drm_for_each_connector_iter(connector, iter) \
 	while ((connector = drm_connector_list_iter_next(iter)))