RDMA/ucma: Use struct_size() helper

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/ucma.c

@@ -951,8 +951,7 @@ static ssize_t ucma_query_path(struct ucma_context *ctx,
 		}
 	}
 
-	if (copy_to_user(response, resp,
-			 sizeof(*resp) + (i * sizeof(struct ib_path_rec_data))))
+	if (copy_to_user(response, resp, struct_size(resp, path_data, i)))
 		ret = -EFAULT;
 
 	kfree(resp);