iwlwifi: mvm: d3: use struct_size() in kzalloc()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
	int stuff;
        void *entry[];
};

instance = kzalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

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

drivers/net/wireless/intel/iwlwifi/mvm/d3.c

@@ -1811,8 +1811,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
 		n_matches = 0;
 	}
 
-	net_detect = kzalloc(sizeof(*net_detect) +
-			     (n_matches * sizeof(net_detect->matches[0])),
+	net_detect = kzalloc(struct_size(net_detect, matches, n_matches),
 			     GFP_KERNEL);
 	if (!net_detect || !n_matches)
 		goto out_report_nd;
@@ -1827,8 +1826,7 @@ static void iwl_mvm_query_netdetect_reasons(struct iwl_mvm *mvm,
 		for (j = 0; j < SCAN_OFFLOAD_MATCHING_CHANNELS_LEN; j++)
 			n_channels += hweight8(fw_match->matching_channels[j]);
 
-		match = kzalloc(sizeof(*match) +
-				(n_channels * sizeof(*match->channels)),
+		match = kzalloc(struct_size(match, channels, n_channels),
 				GFP_KERNEL);
 		if (!match)
 			goto out_report_nd;