staging: comedi: ni_stc.h: remove boardtype macro

This macro relies on a local variable having a specific name and
returns an object that variable points to. This object is the
boardinfo used by the driver.

The comedi core provides the comedi_board() helper to return a
const pointer to the boardinfo. Remove the 'boardtype' macro and
fix all the users of the 'boardtype' macro to use the comedi_board()
helper to get the const boardinfo pointer.

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>