f2fs: show compression in statx

fstest reports below message when compression is on:

generic/424 1s ... - output mismatch
    --- tests/generic/424.out
    +++ results/generic/424.out.bad
    @@ -1,2 +1,26 @@
     QA output created by 424
    +[!] Attribute compressed should be set
    +Failed
    +stat_test failed
    +[!] Attribute compressed should be set
    +Failed
    +stat_test failed

We missed to set STATX_ATTR_COMPRESSED on compressed inode in getattr(),
fix it.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>