zeroplus-logic-cube: move USB VID:PID check in scan before device access

zeroplus-logic-cube: move USB VID:PID check in scan before device access

Getting USB strings from faulty devices can be troublesome. Users report
segfaults when unrelated(!) devices get accessed during scan for certain
measurement devices.

Move the VID:PID check during scan before the USB string access. This
avoids access to unrelated devices.

Rephrase the check whether a USB device is a supported model. The
previous implementation's operation is questioned, the loop condition
looked suspicious.

Reported-By: Marek Antoniak <redacted> [the early check]