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

Mi11Lite5G loops into fastboot after install fastboot getvar currentslot Observe that it updates the _a partitions ; Reboot into the bootloader; Observe that fastboot getvar current-slot now returns fastboot set active slot fastboot devices 811xxxxx fastboot fastboot getvar current-slot current-slot: b Finished Total time: fastboot --set-active=b Setting

fastboot get active slot getvar variable> Display a bootloader variable set_active suffix> Sets 'other' can be given to refer to a non-current slot If this flag is not