fx2lafw: Use physical USB connection instead of sdi->index

Previously, sdi->index was used to tell several identical fx2lafw-compatible
devices apart. This was a bit of a hack, so this patch makes it use physical
device connections instead. They're guaranteed to remain the same even if
the USB device reconnects.
zeroplus-logic-cube: Use physical USB connection instead of sdi->index
hantek-dso: Use physical USB connection instead of sdi->index
Remove sdi->index from openbench-logic-sniffer and pipistrello-ols
saleae-logic16: Use physical USB connection instead of sdi->index
Removal of sdi->index, step 1: remove it from headers and helper funcs
Removal of sdi->index, step 2: remove it from sr_session_load()
Removal of sdi->index, step 3: sr_dev_inst_new() calls for input mods
Removal of sdi->index, step 4: fix trivial sr_dev_inst_new() calls
Removal of sdi->index, step 5: fix ikalogic-scanalogic2
Removal of sdi->index, step 6: fix sysclk-lwla
Removal of sdi->index, step 7: fix testo
Removal of sdi->index, step 8: fix victor-dmm