staging: comedi: amplc_pc236: absorb pc236_pci_common_attach()

Absorb `pc236_pci_common_attach()` into `pc236_auto_attach()` since
that's the only place it is called from.

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>