staging: comedi: gsc_hpdi: use PCI_DEVICE_SUB()

Use the `PCI_DEVICE_SUB()` macro in the initializer of the PCI module
device table `gsc_hpdi_pci_table[]`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>