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

output from fastboot getvar all : security-patch-level: current-slot:b

Observe that it updates the _a partitions ; Reboot into the bootloader; Observe that fastboot getvar current-slot now returns

fastboot_ error_ failed to identify current slot Get active system slot fastboot getvar current-slot fastboot getvar all Get active system slot

fastboot get active slot Boot your smartphone into Fastboot Mode · Now, connect your smartphone to the PC using a USB cable · Open a Command Prompt, Terminal, or