staging: comedi: ni_labpc: fix common detach

`labpc_common_detach()` calls `comedi_pci_disable()` unconditionally.
That's okay for PCI devices and harmless for ISA devices (as the
`hw_dev` member will be NULL so `comedi_to_pci_dev()` will return NULL
and `comedi_pci_disable()` checks for that), but it is disastrous for
PCMCIA devices.  Those are managed by the "ni_labpc_cs" module but it
calls this `labpc_common_detach()` and the `hw_dev` member will be
pointing to the `struct device` embedded in a `struct pcmcia_device` in
that case.  That's enough to confuse `comedi_pci_disable()` into
thinking it's a valid PCI device to be disabled.

Use the private board information (`thisboard`) to make sure it is a PCI
device before calling `comedi_pci_disable()`.

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