trivial: Clear the device checksums only if the plugin implements verify()
trivial: Clear the device checksums only if the plugin implements verify()

This ensures that plugins that set the checksums in probe() or setup() don't
get erased by accident.

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