dm zoned: remove duplicate nr_rnd_zones increase in dmz_init_zone()

zmd->nr_rnd_zones was increased twice by mistake. The other place it
is increased in dmz_init_zone() is the only one needed:

1131                 zmd->nr_useable_zones++;
1132                 if (dmz_is_rnd(zone)) {
1133                         zmd->nr_rnd_zones++;
					^^^
Fixes: 3b1a94c8 ("dm zoned: drive-managed zoned block device target")
Cc: stable@vger.kernel.org
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>