btrfs: Add noenospc_debug mount option.

Add noenospc_debug mount option to disable ENOSPC debug with
remount option.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index 7254cf5..13a7cac 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -108,8 +108,9 @@
 	performance impact.  (The fstrim command is also available to
 	initiate batch trims from userspace).
 
+  noenospc_debug(*)
   enospc_debug
-	Debugging option to be more verbose in some ENOSPC conditions.
+	Disable/enable debugging option to be more verbose in some ENOSPC conditions.
 
   fatal_errors=<action>
 	Action to take when encountering a fatal error: