uwb: 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uwb/drp-ie.c

@@ -125,9 +125,8 @@ static struct uwb_ie_drp *uwb_drp_ie_alloc(void)
 {
 	struct uwb_ie_drp *drp_ie;
 
-	drp_ie = kzalloc(sizeof(struct uwb_ie_drp) +
-			UWB_NUM_ZONES * sizeof(struct uwb_drp_alloc),
-			GFP_KERNEL);
+	drp_ie = kzalloc(struct_size(drp_ie, allocs, UWB_NUM_ZONES),
+			 GFP_KERNEL);
 	if (drp_ie)
 		drp_ie->hdr.element_id = UWB_IE_DRP;
 	return drp_ie;