btrfs: define compression levels statically

The maximum and default levels do not change and can be defined
directly. The set_level callback was a temporary solution and will be
removed.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/lzo.c

@@ -523,4 +523,6 @@ const struct btrfs_compress_op btrfs_lzo_compress = {
 	.decompress_bio		= lzo_decompress_bio,
 	.decompress		= lzo_decompress,
 	.set_level		= lzo_set_level,
+	.max_level		= 1,
+	.default_level		= 1,
 };