net: openvswitch: Use struct_size()

Use struct_size() instead of hand writing it.
This is less verbose and more robust.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/e5122b4ff878cbf3ed72653a395ad5c4da04dc1e.1697264974.git.christophe.jaillet@wanadoo.frSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/openvswitch/flow_table.c

@@ -220,16 +220,13 @@ static struct mask_array *tbl_mask_array_alloc(int size)
 	struct mask_array *new;
 
 	size = max(MASK_ARRAY_SIZE_MIN, size);
-	new = kzalloc(sizeof(struct mask_array) +
-		      sizeof(struct sw_flow_mask *) * size +
+	new = kzalloc(struct_size(new, masks, size) +
 		      sizeof(u64) * size, GFP_KERNEL);
 	if (!new)
 		return NULL;
 
 	new->masks_usage_zero_cntr = (u64 *)((u8 *)new +
-					     sizeof(struct mask_array) +
-					     sizeof(struct sw_flow_mask *) *
-					     size);
+					     struct_size(new, masks, size));
 
 	new->masks_usage_stats = __alloc_percpu(sizeof(struct mask_array_stats) +
 						sizeof(u64) * size,