Btrfs: Fix oops for defrag with compression turned on

When we defrag a file, whose size can be fit into an inline extent,
with compression enabled, the compress type is set to be
fs_info->compress_type, which is 0 if the btrfs filesystem is mounted
without compress option. This leads to oops.

Reported-by: Daniel Blueman <daniel.blueman@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>