dm: use vmalloc_array() to simplify code

Remove array_size() calls and replace vmalloc() with vmalloc_array() to
simplify the code.

Signed-off-by: Qianfeng Rong <[e-mail]>
Signed-off-by: Mikulas Patocka <[e-mail]>

drivers/md/dm-cache-policy-smq.c

···
 	nr_buckets = roundup_pow_of_two(max(nr_entries / 4u, 16u));
 	ht->hash_bits = __ffs(nr_buckets);
 
-	ht->buckets = vmalloc(array_size(nr_buckets, sizeof(*ht->buckets)));
+	ht->buckets = vmalloc_array(nr_buckets, sizeof(*ht->buckets));
 	if (!ht->buckets)
 		return -ENOMEM;
 

drivers/md/dm-region-hash.c

···
 	rh->shift = RH_HASH_SHIFT;
 	rh->prime = RH_HASH_MULT;
 
-	rh->buckets = vmalloc(array_size(nr_buckets, sizeof(*rh->buckets)));
+	rh->buckets = vmalloc_array(nr_buckets, sizeof(*rh->buckets));
 	if (!rh->buckets) {
 		DMERR("unable to allocate region hash bucket memory");
 		kfree(rh);

drivers/md/dm-switch.c

···
 		return -EINVAL;
 	}
 
-	sctx->region_table = vmalloc(array_size(nr_slots,
-						sizeof(region_table_slot_t)));
+	sctx->region_table = vmalloc_array(nr_slots,
+					   sizeof(region_table_slot_t));
 	if (!sctx->region_table) {
 		ti->error = "Cannot allocate region table";
 		return -ENOMEM;

drivers/md/dm-thin.c

···
 	}
 
 	pool->cell_sort_array =
-		vmalloc(array_size(CELL_SORT_ARRAY_SIZE,
-				   sizeof(*pool->cell_sort_array)));
+		vmalloc_array(CELL_SORT_ARRAY_SIZE,
+			      sizeof(*pool->cell_sort_array));
 	if (!pool->cell_sort_array) {
 		*error = "Error allocating cell sort array";
 		err_p = ERR_PTR(-ENOMEM);