IB/hfi1: 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, in particular in the
context in which this code is being used.

So, replace the following form:

sizeof(struct opa_port_status_rsp) + num_vls * sizeof(struct _vls_pctrs)

with:

struct_size(rsp, vls, num_vls)

and so on...

Also, notice that variable size is unnecessary, hence it is removed.

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

drivers/infiniband/hw/hfi1/mad.c

@@ -2744,8 +2744,7 @@ static int pma_get_opa_portstatus(struct opa_pma_mad *pmp,
 	u16 link_width;
 	u16 link_speed;
 
-	response_data_size = sizeof(struct opa_port_status_rsp) +
-				num_vls * sizeof(struct _vls_pctrs);
+	response_data_size = struct_size(rsp, vls, num_vls);
 	if (response_data_size > sizeof(pmp->data)) {
 		pmp->mad_hdr.status |= OPA_PM_STATUS_REQUEST_TOO_LARGE;
 		return reply((struct ib_mad_hdr *)pmp);
@@ -3014,8 +3013,7 @@ static int pma_get_opa_datacounters(struct opa_pma_mad *pmp,
 	}
 
 	/* Sanity check */
-	response_data_size = sizeof(struct opa_port_data_counters_msg) +
-				num_vls * sizeof(struct _vls_dctrs);
+	response_data_size = struct_size(req, port[0].vls, num_vls);
 
 	if (response_data_size > sizeof(pmp->data)) {
 		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;
@@ -3232,8 +3230,7 @@ static int pma_get_opa_porterrors(struct opa_pma_mad *pmp,
 		return reply((struct ib_mad_hdr *)pmp);
 	}
 
-	response_data_size = sizeof(struct opa_port_error_counters64_msg) +
-				num_vls * sizeof(struct _vls_ectrs);
+	response_data_size = struct_size(req, port[0].vls, num_vls);
 
 	if (response_data_size > sizeof(pmp->data)) {
 		pmp->mad_hdr.status |= IB_SMP_INVALID_FIELD;