staging: comedi: amplc_pc236: Fix PCI ref count

When attaching a PCI device manually via the comedi driver `attach` hook
(`pc236_attach()`) (called by the comedi core for the `COMEDI_DEVCONFIG`
ioctl), its reference count is incremented in the `for_each_pci_dev`
loop (in `pc236_find_pci_dev()`).  It is decremented when the `detach`
hook (`pc236_detach()`) is called to detach the device.  However, when
the PCI device is attached automatically via the `attach_pci` hook
(`pc236_attach_pci()`, called at probe time via
`comedi_pci_auto_config()`) it's reference count is not incremented so
there will be an unmatched decrement when detaching the device.

Increment the PCI device reference count in `pc236_attach_pci()` to
correct the mismatch.

Once support for manual configuration has been removed from this driver,
the calls to `pci_dev_get()` and `pci_dev_put()` can be removed.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>