Cleanup: replace hard-wired $(AR) 'crv' settings by $(ARFLAGS)

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/siemens/SMN42/Makefile b/board/siemens/SMN42/Makefile
index 2c7b54b..4e75b6f 100644
--- a/board/siemens/SMN42/Makefile
+++ b/board/siemens/SMN42/Makefile
@@ -33,7 +33,7 @@
 SOBJS	:= $(addprefix $(obj),$(SOBJTS))
 
 $(LIB):	$(obj).depend $(OBJS) $(SOBJS)
-	$(AR) crv $@ $(OBJS) $(SOBJS)
+	$(AR) $(ARFLAGS) $@ $(OBJS) $(SOBJS)
 
 clean:
 	rm -f $(SOBJS) $(OBJS)