HID: google: Use struct_size() helper in kzalloc()

Make use of the struct_size() helper instead of an open-coded version,
in order to avoid any potential type mistakes or integer overflows that,
in the worst scenario, could lead to heap overflows.

Also, address the following sparse warnings:
drivers/hid/hid-google-hammer.c:61:23: warning: using sizeof on a flexible structure

Link: https://github.com/KSPP/linux/issues/174
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-google-hammer.c

@@ -58,7 +58,7 @@ static int cbas_ec_query_base(struct cros_ec_device *ec_dev, bool get_state,
 	struct cros_ec_command *msg;
 	int ret;
 
-	msg = kzalloc(sizeof(*msg) + max(sizeof(u32), sizeof(*params)),
+	msg = kzalloc(struct_size(msg, data, max(sizeof(u32), sizeof(*params))),
 		      GFP_KERNEL);
 	if (!msg)
 		return -ENOMEM;