staging: comedi: ni_tio.h: tidy up struct ni_gpct_device

Fix the checkpatch.pl issues:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
CHECK: spinlock_t definition without comment

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>