btrfs: use raid_attr table for btrfs_bg_type_to_factor

The factor is the number of copies.
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -7586,10 +7586,9 @@ void btrfs_reset_fs_info_ptr(struct btrfs_fs_info *fs_info)
  */
 int btrfs_bg_type_to_factor(u64 flags)
 {
-	if (flags & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1 |
-		     BTRFS_BLOCK_GROUP_RAID10))
-		return 2;
-	return 1;
+	const int index = btrfs_bg_flags_to_raid_index(flags);
+
+	return btrfs_raid_array[index].ncopies;
 }