staging: comedi: ni_tio: tidy up ni_tio_set_sync_mode()

The 'force_alt_sync' paramater is always 0. Remove it.

Absorb the GI_ALT_SYNC() inline helper and use some local variables
to clarify this function.

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>