zonefs: Fix active zone accounting

If a file zone transitions to the offline or readonly state from an
active state, we must clear the zone active flag and decrement the
active seq file counter. Do so in zonefs_account_active() using the new
zonefs inode flags ZONEFS_ZONE_OFFLINE and ZONEFS_ZONE_READONLY. These
flags are set if necessary in zonefs_check_zone_condition() based on the
result of report zones operation after an IO error.

Fixes: 87c9ce3f

 ("zonefs: Add active seq file accounting")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>