staging: comedi: addi_apci_3120: cleanup addi_find_boardinfo()

This driver uses the comedi PCI auto attach mechanism and the comedi
core does not use the boardinfo during the attach.

Now that this driver has the attach separated from addi_common.c we
can remove passing the boardinfo in the comedi_driver and cleanup
the code that finds the boardinfo.

Also, rename addi_find_boardinfo() so it has namespace associated
with this driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>