drm/doc: use preferred struct reference in kernel-doc

sed -e 's/\( \* .*\)struct &\([_a-z]*\)/\1\&struct \2/' -i

Originally I wasnt a friend of this style because I thought a
line-break between the "&struct" and "foo" part would break it. But a
quick test shows that " * &struct \n * foo\n" works pefectly well with
current kernel-doc. So time to mass-apply these changes!

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1483044517-5770-6-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_plane_helper.c

@@ -60,7 +60,7 @@
  * Again drivers are strongly urged to switch to the new interfaces.
  *
  * The plane helpers share the function table structures with other helpers,
- * specifically also the atomic helpers. See struct &drm_plane_helper_funcs for
+ * specifically also the atomic helpers. See &struct drm_plane_helper_funcs for
  * the details.
  */