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.

Reported-by:  <syzbot+07efed3bc5a1407bd742@syzkaller.appspotmail.com>
Signed-off-by: F.A. SULAIMAN <asha.16@itfac.mrt.ac.lk>
Reviewed-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>