staging: comedi: adv_pci1710: single source triggers are unique

If a single source trigger passes "step 1" of the do_cmdtest function
they are already unique. There is no need to recheck them.

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