remove nvic.o from stm32/f[24]'s explicit list

this was missed out in 75c216582, see there for details

lib/stm32/f2/Makefile

@@ -28,7 +28,7 @@ CFLAGS		= -Os -g -Wall -Wextra -I../../../include -fno-common \
 		  -ffunction-sections -fdata-sections -MD -DSTM32F2
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= rcc.o gpio.o usart.o spi.o flash.o nvic.o \
+OBJS		= rcc.o gpio.o usart.o spi.o flash.o \
 		  i2c.o exti.o timer.o
 
 VPATH += ../../usb:../:../../cm3

lib/stm32/f4/Makefile

@@ -29,7 +29,7 @@ CFLAGS		= -Os -g -Wall -Wextra -I../../../include -fno-common \
 		  -ffunction-sections -fdata-sections -MD -DSTM32F4
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
-OBJS		= rcc.o gpio.o usart.o spi.o flash.o nvic.o \
+OBJS		= rcc.o gpio.o usart.o spi.o flash.o \
 		  i2c.o exti.o pwr.o timer.o \
 		  usb.o usb_standard.o usb_control.o usb_f107.o