btrfs: fix replace/scrub failure with metadata_uuid

Fstests with POST_MKFS_CMD="btrfstune -m" (as in the mailing list)
reported a few of the test cases failing.

The failure scenario can be summarized and simplified as follows:

  $ mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb1 /dev/sdb2 :0
  $ btrfstune -m /dev/sdb1 :0
  $ wipefs -a /dev/sdb1 :0
  $ mount -o degraded /dev/sdb2 /btrfs :0
  $ btrfs replace start -B -f -r 1 /dev/sdb1 /btrfs :1
    STDERR:
    ERROR: ioctl(DEV_REPLACE_START) failed on "/btrfs": Input/output error

  [11290.583502] BTRFS warning (device sdb2): tree block 22036480 mirror 2 has bad fsid, has 99835c32-49f0-4668-9e66-dc277a96b4a6 want da40350c-33ac-4872-92a8-4948ed8c04d0
  [11290.586580] BTRFS error (device sdb2): unable to fix up (regular) error at logical 22020096 on dev /dev/sdb8 physical 1048576

As above, the replace is failing because we are verifying the header with
fs_devices::fsid instead of fs_devices::metadata_uuid, despite the
metadata_uuid actually being present.

To fix this, use fs_devices::metadata_uuid. We copy fsid into
fs_devices::metadata_uuid if there is no metadata_uuid, so its fine.

Fixes: a3ddbaeb

 ("btrfs: scrub: introduce a helper to verify one metadata block")
CC: stable@vger.kernel.org # 6.4+
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>