block: remove disk_zone_is_full()

block: remove disk_zone_is_full()

The helper function disk_zone_is_full() is only used in
disk_zone_wplug_is_full(). So remove it and open code it directly in
this single caller.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>