trivial: dell-dock: check for valid dock type on open
trivial: dell-dock: check for valid dock type on open

Only add instance ID if it actually probes properly.

Otherwise this makes an invalid assumption that the device is a WD19
EC just because it had the correct hub in front.

Instead check the first time it's opened that the correct device
is identified (`EXPECTED_DOCK_TYPE`)

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