drm/doc: Appease sphinx

Mostly this is unexpected indents. But really it's just a
demonstration for my patch, all these issues have been found&fixed
using the correct source file and line number support I just added.
All line numbers have been perfectly accurate.

One issue looked a bit fishy in intel_lrc.c, where I don't quite grok
what sphinx is unhappy about. But since that file looks like it has
never seen a proper kernel-doc parser I figured better to fix in a
separate path.

v2: Use fancy new &drm_device->struct_mutex linking (Jani).

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/drm_gem.c

@@ -787,7 +787,7 @@ EXPORT_SYMBOL(drm_gem_object_release);
  * @kref: kref of the object to free
  *
  * Called after the last reference to the object has been lost.
- * Must be called holding struct_ mutex
+ * Must be called holding &drm_device->struct_mutex.
  *
  * Frees the object
  */