f2fs: do not set compression bit if kernel doesn't support

If kernel doesn't have CONFIG_F2FS_FS_COMPRESSION, a file having FS_COMPR_FL via
ioctl(FS_IOC_SETFLAGS) is unaccessible due to f2fs_is_compress_backend_ready().
Let's avoid it.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>