main/postmarketos-mkinitfs: fix USB idVendor/idProduct values for ConfigFS

ConfigFS expects idVendor and idProduct values to be prefixed with 0x.

Without this change, google-crosshatch shows as a device with 0:0 as the idVendor/idProduct in lsusb:

Bus 001 Device 004: ID 0000:0000

This confuses VirtualBox: it has trouble detaching this device from a virtual machine, so one must manually use ifconfig to bring down the old USB network connection before reattaching.

With this change, the idVendor/idProduct is correct:

Bus 001 Device 004: ID 18d1:d001 Google Inc.

This issue also seems to affect other devices with ConfigFS, such as the Nexus 5: note that the Nexus 5 also shows up as 0000:0000.

https://matrix.to/#/!clcCCNrLZYwdfNqkkR:disroot.org/$15487159511194991apGpy:matrix.org