f2fs: fix wrong return value of f2fs_bmap_compress()

If compression is disable, we should return zero rather than -EOPNOTSUPP
to indicate f2fs_bmap() is not supported.

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