staging: comedi: ni_atmio: fix license warning.

Resolving license check warning for drivers/staging/comedi. Added the
license definitions present in the rest of the module and made sure it's
aligned with the license (GPL) in the comments for the affected file
(ni_atmio.c). Original warning:

WARNING: modpost: missing MODULE_LICENSE() in drivers/staging/comedi//drivers/ni_atmio.o
see include/linux/module.h for more information.

No longer present after change.

Signed-off-by: Matthew Giassa <matthew@giassa.net>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>