btrfs: consolidate uuid comparisons in btrfs_validate_super

There are three ways the fsid is validated in btrfs_validate_super():

- verify that super_copy::fsid is the same as fs_devices::fsid

- if the metadata_uuid flag is set, verify if super_copy::metadata_uuid
  and fs_devices::metadata_uuid are the same.

- a few lines below, often missed out, verify if dev_item::fsid is the
  same as fs_devices::metadata_uuid.

The function btrfs_validate_super() contains multiple if-statements with
memcmp() to check UUIDs. This patch consolidates them into a single
location.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -2399,6 +2399,14 @@ int btrfs_validate_super(struct btrfs_fs_info *fs_info,
 		ret = -EINVAL;
 	}
 
+	if (memcmp(fs_info->fs_devices->metadata_uuid, sb->dev_item.fsid,
+		   BTRFS_FSID_SIZE) != 0) {
+		btrfs_err(fs_info,
+			"dev_item UUID does not match metadata fsid: %pU != %pU",
+			fs_info->fs_devices->metadata_uuid, sb->dev_item.fsid);
+		ret = -EINVAL;
+	}
+
 	/*
 	 * Artificial requirement for block-group-tree to force newer features
 	 * (free-space-tree, no-holes) so the test matrix is smaller.
@@ -2411,14 +2419,6 @@ int btrfs_validate_super(struct btrfs_fs_info *fs_info,
 		ret = -EINVAL;
 	}
 
-	if (memcmp(fs_info->fs_devices->metadata_uuid, sb->dev_item.fsid,
-		   BTRFS_FSID_SIZE) != 0) {
-		btrfs_err(fs_info,
-			"dev_item UUID does not match metadata fsid: %pU != %pU",
-			fs_info->fs_devices->metadata_uuid, sb->dev_item.fsid);
-		ret = -EINVAL;
-	}
-
 	/*
 	 * Hint to catch really bogus numbers, bitflips or so, more exact checks are
 	 * done later