staging: comedi: addi_apci_16xx: cleanup addi_find_boardinfo()

This function was originally in the addi-data "common" code and
required using pointer math to access the boardinfo data using
the void * 'dev->driver->board_name'. Now that the function is
local to this driver we can access the boardinfo directly and
remove the pointer math.

Rename the function so it has namespace associated with this
driver.

Also, for aesthetic reasons, globally rename the local variable used
for the boardinfo pointer from 'this_board' to 'board',

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>