staging: comedi: amplc_pc236: check bus type before accessing LCR

The PCI-local bridge LCR registers are (assumed to be) present and used
iff the board is a PCI board (a PCI236).  Currently the code tests if
devpriv->lcr_iobase is valid before accessing the registers.  Instead,
check if the board is a PCI board and assume devpriv->lcr_iobase is
valid if so.  (Currently, no validity check is performed as the PCI
vendor and device ID ought to suffice, but simple checks could be added
when attaching the device.)

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