Makefile: remove _all_ the object files in the clean target

For instance eeprom.o is still around after "make clean" without this
change.

Makefile

@@ -3,7 +3,7 @@ CFLAGS=-g -I. -Wall -O2
 all: eeprog 
 
 clean: 
-	rm -f eeprog 24cXX.o
+	rm -f eeprog *.o
 
 eeprog: eeprog.o 24cXX.o