Drop the condition in verify_one_dev_extent,
btrfs_device::disk_total_bytes is set even for a seed device. The
comment is wrong, the size is properly set when cloning the device.

Commit 1b3922a8 ("btrfs: Use real device structure to verify
dev extent") introduced it but it's unclear why the total_disk_bytes
was 0.

Theoretically, all devices (including missing and seed) marked with the
BTRFS_DEV_STATE_IN_FS_METADATA flag gets the total_disk_bytes updated at
fill_device_from_item():

  open_ctree()
    btrfs_read_chunk_tree()
      read_one_dev()
        open_seed_device()
        fill_device_from_item()

Even if verify_one_dev_extent() reports total_disk_bytes == 0, then its
a bug to be fixed somewhere else and not in verify_one_dev_extent() as
it's just a messenger. It is never expected that a total_disk_bytes
shall be zero.

The function fill_device_from_item() does the job of reading it from the
item and updating btrfs_device::disk_total_bytes. So both the missing
device and the seed devices do have their disk_total_bytes updated.
btrfs_find_device can also return a device from fs_info->seed_list
because it searches it as well.

Furthermore, while removing the device if there is a power loss, we
could have a device with its total_bytes = 0, that's still valid.

Instead, introduce a check against maximum block device size in
read_one_dev().
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>