Btrfs: avoid unnecessarily locking inode when clearing a range

If the range being cleared was not marked for defrag and we are not
about to clear the range from the defrag status, we don't need to
lock and unlock the inode.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Chris Mason <clm@fb.com>
Reviewed-by: Wang Shilong <wangshilong1991@gmail.com>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>