btrfs: use ioctl args support mask for subvolume create/delete

Using the defined mask instead of flag enumeration in the ioctl handler
is preferred. No functional changes.
Reviewed-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -1838,9 +1838,7 @@ static noinline int btrfs_ioctl_snap_create_v2(struct file *file,
 		return PTR_ERR(vol_args);
 	vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
 
-	if (vol_args->flags &
-	    ~(BTRFS_SUBVOL_CREATE_ASYNC | BTRFS_SUBVOL_RDONLY |
-	      BTRFS_SUBVOL_QGROUP_INHERIT)) {
+	if (vol_args->flags & ~BTRFS_SUBVOL_CREATE_ARGS_MASK) {
 		ret = -EOPNOTSUPP;
 		goto free_args;
 	}