staging: comedi: contec_pci: remove manual legacy attach

This driver uses the 'attach_pci' callback to attach the pci device
to the comedi subsystem. Since the 'attach' callback is now optional
it can be removed from the driver.

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>