openbench-logic-sniffer: fix acquisition restart with trigger enabled

openbench-logic-sniffer: fix acquisition restart with trigger enabled

With trigger enabled, and with PulseView, a second (or more) acquisition
starts immediately instead of blocking. It's mandatory to try several times
to have a correct behavior.

According to http://mygizmos.org/ols/Logic-Sniffer-FPGA-Spec.pdf section 2.3.1
p.8, the Openbench Logic Sniffer must be reset before each arm command.

This fixes bug #809.

Signed-off-by: Gwenhael Goavec-Merou <redacted>