staging: comedi: ni_660x: remove inline function board()

This function is used to get the dev->board_ptr from the
comedi_device. Remove the function and use a local variable
to hold the pointer where used. Use the comedi_board() helper
to get the 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>