treewide: fix a few typos in comments

- kenrel -> kernel
- whetehr -> whether
- ttt -> tt
- sss -> ss

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

fs/btrfs/relocation.c

@@ -709,7 +709,7 @@ again:
 	WARN_ON(cur->checked);
 	if (!list_empty(&cur->upper)) {
 		/*
-		 * the backref was added previously when processsing
+		 * the backref was added previously when processing
 		 * backref of type BTRFS_TREE_BLOCK_REF_KEY
 		 */
 		BUG_ON(!list_is_singular(&cur->upper));