wacom-usb: Un-pack the descriptor to fix -Waddress-of-packed-member warnings
wacom-usb: Un-pack the descriptor to fix -Waddress-of-packed-member warnings

This isn't read in-situ since switching to fu_common_read_uintXX_safe()
and it's only used to calculate the size of the block.

fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd