staging: comedi: amplc_dio200: no need to manipulate PCI ref count

Now that this driver no longer supports "manual" attachment of PCI
devices in its `attach` hook (`dio200_attach()`), it no longer has code
that searches for a suitable PCI device and increments its reference
count.  Since the driver no longer has any reason for incrementing and
decrementing the PCI device's reference count, 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>