Looking at the --bitfury-clockbits code, the slot (or bank) is needed also, as in api call, so the arg format should be like bank:chip:speed.
Looking at it too. Got the core dump at line 388 ... probably just uninitialised variable ... will see
EDIT: Fix committed - command line option working too
EDIT2: Now you can define the number of boards too so in bitfury-config.h for BFSB boards use:
#define BITFURY_BOARDCHIPS 16
#define BITFURY_BANKBOARDS 4
#define BITFURY_MAXBANKS 4