V4L/DVB (5877): radio-gemtek-pci: remove unused structure member

The drivers reads the PCI subsystem ID into its state structure, but it's
never used anywhere.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>