[media] cx231xx: Paranoic stack memory save

Saves 255 bytes of stack memory on cx231xx_usb_probe() by removing a char array.

Tested by compilation only.

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>