rtc-m48t59: fix setting of a year on m48t08 and m48t02 rtcs

Fix setting of a year in m48t08 and m48t02 clocks.
They do not have century bits and setting them
causes the year to overflow (bit 0x80 set).

Problem found by Robert Reif on Sun Sparcstation 20.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>