staging: comedi: ni_670x: remove thisboard and devpriv macros

staging: comedi: ni_670x: remove thisboard and devpriv macros

The 'thisboard' and 'devpriv' macros rely on a local variable having
a specific name and yield pointers derived from that local variable.
Replace the macros with local variables where used. Use the
comedi_board() helper to get the 'thisboard' 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>