staging: comedi: addi_apci_1516: cleanup apci1516_detach()

This driver uses the comedi auto_config mechanism to attach to
the comedi subsystem. The dev->hw_dev is set by the core so
comedi_to_pci_dev() will always return a valid pcidev. Remove
the unnecessary test.

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