btrfs: zoned: fix zone finishing with missing devices

If do_zone_finish() is called with a filesystem that has missing devices
(e.g. a RAID file system mounted in degraded mode) it is accessing the
btrfs_device::zone_info pointer, which will not be set if the device
in question is missing.

Check if the device is present (by checking if it has a valid block device
pointer associated) and if not, skip zone finishing for it.

Fixes: 4dcbb8ab ("btrfs: zoned: make zone finishing multi stripe capable")
CC: stable@vger.kernel.org # 6.1+
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>