Input: wacom - check for allocation failure in probe()

We accidentally removed the check for NULL in 3aac0ef "Input: wacom -
isolate input registration".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Bagwell <chris@cnpbagwell.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/tablet/wacom_sys.c

@@ -1002,6 +1002,8 @@ static int wacom_probe(struct usb_interface *intf, const struct usb_device_id *i
 		return -EINVAL;
 
 	wacom = kzalloc(sizeof(struct wacom), GFP_KERNEL);
+	if (!wacom)
+		return -ENOMEM;
 
 	wacom_wac = &wacom->wacom_wac;
 	wacom_wac->features = *((struct wacom_features *)id->driver_info);