writeback: fix inode cgroup switching comment

Commit 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb
transaction and use it for stat updates") refers to
inode_switch_wb_work_fn() which never got merged.

Switch the comments to inode_switch_wbs_work_fn().

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates")
Signed-off-by: Greg Thelen <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/backing-dev.h

···
 	rcu_read_lock();
 
 	/*
-	 * Paired with store_release in inode_switch_wb_work_fn() and
+	 * Paired with store_release in inode_switch_wbs_work_fn() and
 	 * ensures that we see the new wb if we see cleared I_WB_SWITCH.
 	 */
 	cookie->locked = smp_load_acquire(&inode->i_state) & I_WB_SWITCH;

include/linux/fs.h

···
  * I_WB_SWITCH		Cgroup bdi_writeback switching in progress.  Used to
  *			synchronize competing switching instances and to tell
  *			wb stat updates to grab the i_pages lock.  See
- *			inode_switch_wb_work_fn() for details.
+ *			inode_switch_wbs_work_fn() for details.
  *
  * I_OVL_INUSE		Used by overlayfs to get exclusive ownership on upper
  *			and work dirs among overlayfs mounts.