rtc: Remove 2nd reference to max6900.o in drivers/rtc/Makefile

Signed-off-by: Stefan Roese <sr@denx.de>

drivers/rtc/Makefile

@@ -43,7 +43,6 @@ COBJS-$(CONFIG_RTC_ISL1208) += isl1208.o
 COBJS-y += m41t11.o
 COBJS-y += m41t60.o
 COBJS-$(CONFIG_RTC_M41T62) += m41t62.o
-COBJS-y += max6900.o
 COBJS-y += m48t35ax.o
 COBJS-y += max6900.o
 COBJS-y += mc146818.o