getvar: fix broken 'fastboot flash' when partition has slots

FP3 installation : stuck in fastboot mode - Setup fastboot getvar currentslot 00:00 Prerequisites 05:16 Check and Change Current Slot on Android via Fastboot 10:14 fastboot change slot fastboot getvar current-slot > check slot is a or b, and my device show the slot on b fastboot set_active a > change the slot from b to a 8

fastboot set active slot Xiaomi Mi A2$ fastboot getvar current-slot current-slot: a finished total time: mf@mf-OptiPlex-3040:~PulpitXiaomi Mi A2$ fastboot