f2fs: remove redundant check in f2fs_sanity_check_cluster

It have checked "compressed" at the entry of
f2fs_sanity_check_cluster, just remove the
redundant check for better performance here.

Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>