Input: evdev - use struct_size() in kzalloc() and vzalloc()

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 size 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: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/evdev.c

@@ -503,14 +503,13 @@ static int evdev_open(struct inode *inode, struct file *file)
 {
 	struct evdev *evdev = container_of(inode->i_cdev, struct evdev, cdev);
 	unsigned int bufsize = evdev_compute_buffer_size(evdev->handle.dev);
-	unsigned int size = sizeof(struct evdev_client) +
-					bufsize * sizeof(struct input_event);
 	struct evdev_client *client;
 	int error;
 
-	client = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
+	client = kzalloc(struct_size(client, buffer, bufsize),
+			 GFP_KERNEL | __GFP_NOWARN);
 	if (!client)
-		client = vzalloc(size);
+		client = vzalloc(struct_size(client, buffer, bufsize));
 	if (!client)
 		return -ENOMEM;