brcmfmac: 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;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = kzalloc(size, 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)

Notice that, in this case, variable reqsz is not necessary,
hence it is removed.

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/broadcom/brcm80211/brcmfmac/firmware.c

@@ -711,7 +711,6 @@ brcmf_fw_alloc_request(u32 chip, u32 chiprev,
 	size_t mp_path_len;
 	u32 i, j;
 	char end = '\0';
-	size_t reqsz;
 
 	for (i = 0; i < table_size; i++) {
 		if (mapping_table[i].chipid == chip &&
@@ -726,8 +725,7 @@ brcmf_fw_alloc_request(u32 chip, u32 chiprev,
 		return NULL;
 	}
 
-	reqsz = sizeof(*fwreq) + n_fwnames * sizeof(struct brcmf_fw_item);
-	fwreq = kzalloc(reqsz, GFP_KERNEL);
+	fwreq = kzalloc(struct_size(fwreq, items, n_fwnames), GFP_KERNEL);
 	if (!fwreq)
 		return NULL;