rtc: mt6397: add compatible for mt6323

use mt6397 rtc driver also for mt6323 but with different
base/size see "mfd: mt6323: add mt6323 rtc+pwrc"

Signed-off-by: Josef Friedl <josef.friedl@speed.at>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>