staging: comedi: cb_pcidas64: remove unnecessary Step 2b test in (*do_cmdtest)

This test is unnecessary. The cfc_check_trigger_src() in Step 1 ensures that
the trigger source is one of these values and Step 2 makes sure it's only one
of these values.

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>