staging: comedi: amplc_pc236: no need to set hw_dev

The call to `comedi_set_hw_dev()` from `pc236_pci_common_attach()` is
now unnecessary since `pc236_pci_common_attach()` is now only called
from this driver's `auto_attach` hook `pc236_auto_attach()` and the
comedi core now calls `comedi_set_hw_dev()` before calling that.  Remove
the unnecessary call.

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>