stm32/desig: include in f4 library

The code is all there and working but simply isn't being built.

lib/stm32/f4/Makefile

@@ -37,7 +37,8 @@ CFLAGS		= -Os -g \
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
 
-OBJS		= adc.o adc_common_v1.o can.o gpio.o pwr.o rcc.o rtc.o crypto.o
+OBJS		= adc.o adc_common_v1.o can.o desig.o gpio.o pwr.o rcc.o \
+		  rtc.o crypto.o
 
 OBJS            += crc_common_all.o dac_common_all.o dma_common_f24.o \
                    gpio_common_all.o gpio_common_f0234.o i2c_common_all.o \