trivial: Fix a warning when compiling the unifying plugin
trivial: Fix a warning when compiling the unifying plugin

hughsie/fwupd,vathpela/fwupd,superm1/fwupd,vathpela/fwupd,superm1/fwupd,fwupd/fwupd,fwupd/fwupd,superm1/fwupd,fwupd/fwupd,hughsie/fwupd,vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,hughsie/fwupd