trivial: Fix a compile warning in the dell plugin
trivial: Fix a compile warning in the dell plugin

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