Commit a95e8c28 "powerpc/defconfig: update RTC support" duplicated
the CONFIG_RTC_DRV_DS1307 symbol in mpc85xx_defconfig and
mpc85xx_smp_defconfig, resulting in this:

arch/powerpc/configs/mpc85xx_smp_defconfig:217:warning: override: reassigning to symbol RTC_DRV_DS1307

Fixes: a95e8c28 "powerpc/defconfig: update RTC support"
Cc: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>