Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 2b6c12e..a24a3f2 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -243,7 +243,7 @@
  * Insert @em into @tree or perform a simple forward/backward merge with
  * existing mappings.  The extent_map struct passed in will be inserted
  * into the tree directly, with an additional reference taken, or a
- * reference dropped if the merge attempt was successfull.
+ * reference dropped if the merge attempt was successful.
  */
 int add_extent_mapping(struct extent_map_tree *tree,
 		       struct extent_map *em)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 93c28a1..80920bc 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2324,7 +2324,7 @@
 
 		/*
 		 * if ret == 0 means we found what we were searching for, which
-		 * is weird, but possible, so only screw with path if we didnt
+		 * is weird, but possible, so only screw with path if we didn't
 		 * find the key and see if we have stuff that matches
 		 */
 		if (ret > 0) {
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 58250e0..199a801 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2346,7 +2346,7 @@
 		root = next->root;
 		BUG_ON(!root);
 
-		/* no other choice for non-refernce counted tree */
+		/* no other choice for non-references counted tree */
 		if (!root->ref_cows)
 			return root;