btrfs: don't drop a reference if btrfs_check_write_meta_pointer() fails

In the zoned mode there's a bug in the extent buffer tree conversion to
xarray. The reference for eb is dropped and code continues but the
references get dropped by releasing the batch.

Reported-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Fixes: 19d7f65f ("btrfs: convert the buffer_radix to an xarray")
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>