dm space map disk: fix sm_disk_count_is_more_than_one()

dm_tm_shadow_block() is the only caller of
dm_sm_count_is_more_than_one() which only ever operates on a metadata
space-map.  So in practice, sm_disk_count_is_more_than_one() isn't
actually used (which explains why this bug never amounted to anything).

But fix sm_disk_count_is_more_than_one() to properly set *result and
return 0.
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/persistent-data/dm-space-map-disk.c

@@ -78,7 +78,9 @@ static int sm_disk_count_is_more_than_one(struct dm_space_map *sm, dm_block_t b,
 	if (r)
 		return r;
 
-	return count > 1;
+	*result = count > 1;
+
+	return 0;
 }
 
 static int sm_disk_set_count(struct dm_space_map *sm, dm_block_t b,