drm/doc: Fix more kerneldoc/sphinx warnings

These are the leftovers I could only track down using keep_warnings =
True. For some of them we might want to update our style guide on how
to reference structures and constants, not sure ...

Cc: Markus Heiser <markus.heiser@darmarit.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-1-git-send-email-daniel.vetter@ffwll.ch
diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index fca1cd1..9f63736 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -210,8 +210,8 @@
  * drm_gem_object_unreference_unlocked().
  *
  * Drivers should never call this directly in their code. Instead they should
- * wrap it up into a driver_gem_object_unreference(struct driver_gem_object
- * *obj) wrapper function, and use that. Shared code should never call this, to
+ * wrap it up into a ``driver_gem_object_unreference(struct driver_gem_object
+ * *obj)`` wrapper function, and use that. Shared code should never call this, to
  * avoid breaking drivers by accident which still depend upon dev->struct_mutex
  * locking.
  */