dm zoned: fix unused but set variable warnings

Fix unused but set variable warnings:

drivers/md/dm-zoned-reclaim.c:504:42: warning:
 variable nr_rnd set but not used [-Wunused-but-set-variable]
  504 |  unsigned int p_unmap, nr_unmap_rnd = 0, nr_rnd = 0;
      |                                          ^~~~~~
drivers/md/dm-zoned-reclaim.c:504:24: warning:
 variable nr_unmap_rnd set but not used [-Wunused-but-set-variable]
  504 |  unsigned int p_unmap, nr_unmap_rnd = 0, nr_rnd = 0;
      |                        ^~~~~~~~~~~~

Fixes: f97809ae ("dm zoned: per-device reclaim")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>