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.