HID: betop: fix slab-out-of-bounds Write in betop_probe

In the Linux kernel, the following vulnerability has been resolved: HID: betop: fix slab-out-of-bounds Write in betop_probe Syzbot reported slab-out-of-bounds Write bug in hid-betopff driver. The problem is the driver assumes the device must have an input report but some malicious devices violate this assumption. So this patch checks hid_device's input is non empty before it's been used.