trivial: Use the new possible_plugin support for USB devices too
trivial: Use the new possible_plugin support for USB devices too

This matches the UDEV device add, and was missed from the original commit due
to a failed rebase.

Fixes https://github.com/fwupd/fwupd/issues/1512

hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd