drm: Add kerneldoc markup for new @scan parameters in drm_mm

A couple of parameters slipped through the kerneldoc net.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161228105120.14500-1-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_mm.c

@@ -619,6 +619,7 @@ EXPORT_SYMBOL(drm_mm_scan_init_with_range);
 
 /**
  * drm_mm_scan_add_block - add a node to the scan list
+ * @scan: the active drm_mm scanner
  * @node: drm_mm_node to add
  *
  * Add a node to the scan list that might be freed to make space for the desired
@@ -701,6 +702,7 @@ EXPORT_SYMBOL(drm_mm_scan_add_block);
 
 /**
  * drm_mm_scan_remove_block - remove a node from the scan list
+ * @scan: the active drm_mm scanner
  * @node: drm_mm_node to remove
  *
  * Nodes _must_ be removed in exactly the reverse order from the scan list as