btrfs: fix string and comment grammatical issues and typos

Signed-off-by: Nicholas D Steeves <nsteeves@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
index e05619f..875c757 100644
--- a/fs/btrfs/struct-funcs.c
+++ b/fs/btrfs/struct-funcs.c
@@ -36,7 +36,7 @@
  *
  * The end result is that anyone who #includes ctree.h gets a
  * declaration for the btrfs_set_foo functions and btrfs_foo functions,
- * which are wappers of btrfs_set_token_#bits functions and
+ * which are wrappers of btrfs_set_token_#bits functions and
  * btrfs_get_token_#bits functions, which are defined in this file.
  *
  * These setget functions do all the extent_buffer related mapping