libnvdimm, btt: add a couple of missing kernel-doc lines

Recent updates to btt.h neglected to add corresponding kernel-doc lines
for new structure members. Add them.
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/btt.h

@@ -125,6 +125,7 @@ struct aligned_lock {
  * @list:		List head for list of arenas
  * @debugfs_dir:	Debugfs dentry
  * @flags:		Arena flags - may signify error states.
+ * @err_lock:		Mutex for synchronizing error clearing.
  *
  * arena_info is a per-arena handle. Once an arena is narrowed down for an
  * IO, this struct is passed around for the duration of the IO.
@@ -176,6 +177,7 @@ struct arena_info {
  * @init_lock:		Mutex used for the BTT initialization
  * @init_state:		Flag describing the initialization state for the BTT
  * @num_arenas:		Number of arenas in the BTT instance
+ * @phys_bb:		Pointer to the namespace's badblocks structure
  */
 struct btt {
 	struct gendisk *btt_disk;