Bug 1153

PV currently pretends to scan a lot more drivers than it can actually use.

DeviceManager::DeviceManager() iterates over *all* drivers and updates the progress bar via "Scanning for %1...". However, the actual scan function driver_scan() that's later used to do the actual scan will (correctly) filter out only LAs and scopes, and not scan anything else.

The progressbar should reflect that, i.e. only print progress for those that were actually scanned, IMHO.

The -l 5 output from libsigrok correctly only emits those drivers that were actually scanned by PV (a lot fewer than for e.g. sigrok-cli).