Fix zdb crash

We have to use umem_free() instead of free() if we are using
umem_zalloc()

Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Igor Kozhukhov <igor@dilos.org>
Closes openzfs#8402

lib/libzpool/util.c

@@ -105,7 +105,7 @@ show_vdev_stats(const char *desc, const char *ctype, nvlist_t *nv, int indent)
 		    vs->vs_space ? 6 : 0, vs->vs_space ? avail : "",
 		    rops, wops, rbytes, wbytes, rerr, werr, cerr);
 	}
-	free(v0);
+	umem_free(v0, sizeof (*v0));
 
 	if (nvlist_lookup_nvlist_array(nv, ctype, &child, &children) != 0)
 		return;
@@ -124,7 +124,7 @@ show_vdev_stats(const char *desc, const char *ctype, nvlist_t *nv, int indent)
 		if (nvlist_lookup_uint64(cnv, ZPOOL_CONFIG_NPARITY, &np) == 0)
 			tname[strlen(tname)] = '0' + np;
 		show_vdev_stats(tname, ctype, cnv, indent + 2);
-		free(tname);
+		umem_free(tname, len);
 	}
 }