rtc: rv3029: annotate init and exit functions

rv30{2,4}9_register_driver and rv30{2,4}9_unregister_driver are only called
from the init and exit functions of the module. Annotate them properly.

Link: https://lore.kernel.org/r/20191223101430.1091572-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>