drm: Fixup flip-work kerneldoc

Describe the fifo parameter. It seems like kerneldoc doesn't properly
handle fields defined using a macro, so it will end up complaining about
this anyway and not generate the documentation for it either. At least
the kerneldoc is now complete.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_flip_work.h

@@ -57,6 +57,7 @@ typedef void (*drm_flip_func_t)(struct drm_flip_work *work, void *val);
  * @count: number of committed items
  * @func: callback fxn called for each committed item
  * @worker: worker which calls @func
+ * @fifo: queue of committed items
  */
 struct drm_flip_work {
 	const char *name;