rtc: mt6397: Remove plaform module alias

The driver uses the MODULE_ALIAS() macro to export a platform module alias
to allow the module to be autoloaded if the device is registered using the
legacy platform registration mechanism but the driver is always used by OF
only machines so the alias is not needed and should just be removed.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>