Staging: comedi: drivers: ni_atmio.c: fixed multi-line derefernce issue

Fixed coding style issue.

Signed-off-by: Pratik Jain <pratik.jain0509@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>