failed build u-boot for rk3399 board

[67113513]

e.g. try a firefly build:
$./make.sh firefly-rk3399, and you can get error:

LD drivers/power/pmic/built-in.o
CC common/xyzModem.o
CC common/rbsb.o
CC common/zm.o
In file included from common/rbsb.c:29:
common/rbsb.c: In function ‘io_mode’:
common/zglobal.h:307:12: error: statement will never be executed [-Werror=switch-unreachable]
307 | #define OK 0
| ^
common/rbsb.c:485:10: note: in expansion of macro ‘OK’
485 | return OK;
| ^~
CC drivers/serial/serial-uclass.o
cc1: all warnings being treated as errors
make[1]: *** [scripts/Makefile.build:280: common/rbsb.o] Error 1
make[1]: *** Waiting for unfinished jobs....
CC drivers/power/regulator/pwm_regulator.o
CC drivers/serial/ns16550.o
CC drivers/power/regulator/fixed.o
CC drivers/power/regulator/rk8xx.o
LD cmd/built-in.o
CC drivers/spi/spi-uclass.o
CC drivers/usb/common/common.o
CC drivers/usb/dwc3/core.o
CC drivers/usb/dwc3/gadget.o
LD drivers/spi/built-in.o
LD drivers/serial/built-in.o
LD drivers/usb/common/built-in.o
CC drivers/usb/eth/usb_ether.o
CC drivers/usb/eth/asix.o
LD drivers/power/regulator/built-in.o
CC drivers/usb/gadget/udc/udc-core.o
CC drivers/usb/gadget/udc/udc-uclass.o
CC drivers/usb/gadget/epautoconf.o
CC drivers/usb/eth/asix88179.o
CC drivers/usb/dwc3/ep0.o
make: *** [Makefile:1307: common] Error 2
make: *** Waiting for unfinished jobs....
CC drivers/usb/eth/mcs7830.o
CC drivers/usb/gadget/config.o
CC drivers/usb/eth/smsc95xx.o
LD drivers/usb/gadget/udc/built-in.o
CC drivers/usb/eth/r8152.o
CC drivers/usb/gadget/usbstring.o
CC drivers/usb/gadget/g_dnl.o
CC drivers/usb/eth/r8152_fw.o
CC drivers/usb/gadget/f_mass_storage.o
CC drivers/usb/gadget/f_fastboot.o
LD drivers/usb/dwc3/dwc3.o
LD drivers/usb/eth/built-in.o
LD drivers/usb/dwc3/built-in.o
LD drivers/usb/gadget/built-in.o

Actually it'a warning but the compilation stopped!