Btrfs: fix typo in convert_extent_bit

It should be convert_extent_bit.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

fs/btrfs/extent_io.c

@@ -933,7 +933,8 @@ int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, int bits,
 
 
 /**
- * convert_extent - convert all bits in a given range from one bit to another
+ * convert_extent_bit - convert all bits in a given range from one bit to
+ * 			another
  * @tree:	the io tree to search
  * @start:	the start offset in bytes
  * @end:	the end offset in bytes (inclusive)