zonefs: Fix file size of zones in full condition

Per ZBC/ZAC/ZNS specifications, write pointers may not have valid values
when zones are in full condition. However, when zonefs mounts a zoned
block device, zonefs refers write pointers to set file size even when
the zones are in full condition. This results in wrong file size. To fix
this, refer maximum file size in place of write pointers for zones in
full condition.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Fixes: 8dcc1a9d ("fs: New zonefs file system")
Cc: <stable@vger.kernel.org> # 5.6+
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>