rndis_wlan: 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 code of the following form:

sizeof(*pmkids) + max_pmkids * sizeof(pmkids->bssid_info[0])

with:

struct_size(pmkids, bssid_info, num_pmkids)

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rndis_wlan.c

@@ -1707,7 +1707,7 @@ static struct ndis_80211_pmkid *get_device_pmkids(struct usbnet *usbdev)
 	int len, ret, max_pmkids;
 
 	max_pmkids = priv->wdev.wiphy->max_num_pmkids;
-	len = sizeof(*pmkids) + max_pmkids * sizeof(pmkids->bssid_info[0]);
+	len = struct_size(pmkids, bssid_info, max_pmkids);
 
 	pmkids = kzalloc(len, GFP_KERNEL);
 	if (!pmkids)
@@ -1740,7 +1740,7 @@ static int set_device_pmkids(struct usbnet *usbdev,
 	int ret, len, num_pmkids;
 
 	num_pmkids = le32_to_cpu(pmkids->bssid_info_count);
-	len = sizeof(*pmkids) + num_pmkids * sizeof(pmkids->bssid_info[0]);
+	len = struct_size(pmkids, bssid_info, num_pmkids);
 	pmkids->length = cpu_to_le32(len);
 
 	debug_print_pmkids(usbdev, pmkids, __func__);
@@ -1761,7 +1761,7 @@ static struct ndis_80211_pmkid *remove_pmkid(struct usbnet *usbdev,
 						struct cfg80211_pmksa *pmksa,
 						int max_pmkids)
 {
-	int i, newlen, err;
+	int i, err;
 	unsigned int count;
 
 	count = le32_to_cpu(pmkids->bssid_info_count);
@@ -1786,9 +1786,7 @@ static struct ndis_80211_pmkid *remove_pmkid(struct usbnet *usbdev,
 		pmkids->bssid_info[i] = pmkids->bssid_info[i + 1];
 
 	count--;
-	newlen = sizeof(*pmkids) + count * sizeof(pmkids->bssid_info[0]);
-
-	pmkids->length = cpu_to_le32(newlen);
+	pmkids->length = cpu_to_le32(struct_size(pmkids, bssid_info, count));
 	pmkids->bssid_info_count = cpu_to_le32(count);
 
 	return pmkids;
@@ -1831,7 +1829,7 @@ static struct ndis_80211_pmkid *update_pmkid(struct usbnet *usbdev,
 	}
 
 	/* add new pmkid */
-	newlen = sizeof(*pmkids) + (count + 1) * sizeof(pmkids->bssid_info[0]);
+	newlen = struct_size(pmkids, bssid_info, count + 1);
 
 	new_pmkids = krealloc(pmkids, newlen, GFP_KERNEL);
 	if (!new_pmkids) {