mISDN: hfcsusb: 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 code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/hardware/mISDN/hfcsusb.c

@@ -262,8 +262,7 @@ hfcsusb_ph_info(struct hfcsusb *hw)
 	struct dchannel *dch = &hw->dch;
 	int i;
 
-	phi = kzalloc(sizeof(struct ph_info) +
-		      dch->dev.nrbchan * sizeof(struct ph_info_ch), GFP_ATOMIC);
+	phi = kzalloc(struct_size(phi, bch, dch->dev.nrbchan), GFP_ATOMIC);
 	phi->dch.ch.protocol = hw->protocol;
 	phi->dch.ch.Flags = dch->Flags;
 	phi->dch.state = dch->state;