staging: comedi: ni_tio: fix ni_tio_arm() params/vars

As suggested by checkpatch.pl:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

The 'arm' parameter is really a true/false flag. For aesthetics,
change it to a bool.

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>