trivial: Only auto-set the device priority if not already set
trivial: Only auto-set the device priority if not already set

If the plugin has set the priority manually do not overwrite the value.

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