btrfs: move fs_info::fs_frozen to the flags

We can keep the state among the other fs_info flags, there's no reason
why fs_frozen would need to be separate.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 53d43cd..2100be6 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2242,7 +2242,7 @@
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
 	struct btrfs_root *root = fs_info->tree_root;
 
-	fs_info->fs_frozen = 1;
+	set_bit(BTRFS_FS_FROZEN, &fs_info->flags);
 	/*
 	 * We don't need a barrier here, we'll wait for any transaction that
 	 * could be in progress on other threads (and do delayed iputs that
@@ -2261,7 +2261,9 @@
 
 static int btrfs_unfreeze(struct super_block *sb)
 {
-	btrfs_sb(sb)->fs_frozen = 0;
+	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
+
+	clear_bit(BTRFS_FS_FROZEN, &fs_info->flags);
 	return 0;
 }