RTC: Fix Makefile problem with COBJS-$(CONFIG_RTC_DS1307 || CONFIG_RTC_DS1338)

This "||" doesn't seem to work. Now using the idea suggest by Scott Wood
to combine both config options into one line. This even allows defining
both options and not generating the target object twice.

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

drivers/rtc/Makefile

@@ -32,7 +32,8 @@ COBJS-y += date.o
 COBJS-$(CONFIG_RTC_DS12887) += ds12887.o
 COBJS-$(CONFIG_RTC_DS1302) += ds1302.o
 COBJS-$(CONFIG_RTC_DS1306) += ds1306.o
-COBJS-$(CONFIG_RTC_DS1307 || CONFIG_RTC_DS1338) += ds1307.o
+COBJS-$(CONFIG_RTC_DS1307)$(CONFIG_RTC_DS1338) += ds1307.o
+COBJS-y += $(COBJS-yy)
 COBJS-$(CONFIG_RTC_DS1337) += ds1337.o
 COBJS-$(CONFIG_RTC_DS1374) += ds1374.o
 COBJS-$(CONFIG_RTC_DS1556) += ds1556.o