btrfs: fix the code comments for LZO compression workspace

Fix the code comments for lzo compression workspace.
The buf item is used to store the decompressed data
and cbuf is used to store the compressed data.
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
Signed-off-by: NJosef Bacik <jbacik@fusionio.com>

fs/btrfs/lzo.c

@@ -31,8 +31,8 @@
 
 struct workspace {
 	void *mem;
-	void *buf;	/* where compressed data goes */
-	void *cbuf;	/* where decompressed data goes */
+	void *buf;	/* where decompressed data goes */
+	void *cbuf;	/* where compressed data goes */
 	struct list_head list;
 };