writeback: update comment in inode_io_list_move_locked

The @head can be wb->b_dirty_time, so update the comment.

Acked-by: Tejun Heo <[e-mail]>
Signed-off-by: Wang Long <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/fs-writeback.c

···
  * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
  * @inode: inode to be moved
  * @wb: target bdi_writeback
- * @head: one of @wb->b_{dirty|io|more_io}
+ * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
  *
  * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
  * Returns %true if @inode is the first occupant of the !dirty_time IO