rtc: gemini: Remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release
or on probe failure

Signed-off-by: Nizam Haider <nijamh@cdac.in>
Acked-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>