Btrfs: cleanup the comment for clear_state_bit in extent_io.c

No 'delete' arg is used for clear_state_bit.
Cleanup the comment.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>

fs/btrfs/extent_io.c

@@ -413,7 +413,7 @@ static struct extent_state *next_state(struct extent_state *state)
 
 /*
  * utility function to clear some bits in an extent state struct.
- * it will optionally wake up any one waiting on this state (wake == 1)
+ * it will optionally wake up any one waiting on this state (wake == 1).
  *
  * If no bits are set on the state struct after clearing things, the
  * struct is freed and removed from the tree