btrfs: zoned: activate block group properly on unlimited active zone device

btrfs_zone_activate() checks if it activated all the underlying zones in
the loop. However, that check never hit on an unlimited activate zone
device (max_active_zones == 0).

Fortunately, it still works without ENOSPC because btrfs_zone_activate()
returns true in the end, even if block_group->zone_is_active == 0. But, it
is confusing to have non zone_is_active block group still usable for
allocation. Also, we are wasting CPU time to iterate the loop every time
btrfs_zone_activate() is called for the blog groups.

Since error case in the loop is handled by out_unlock, we can just set
zone_is_active and do the list stuff after the loop.

Fixes: f9a912a3

 ("btrfs: zoned: make zone activation multi stripe capable")
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>