rtc-x1205: fix rtc_time to y2k register value conversion

The possible CCR_Y2K register values are 19 or 20 and struct rtc_time's
tm_year is in years since 1900.

The function translating rtc_time to register values assumes tm_year to be
years since first christmas, though, and we end up storing 0 or 1 in the
CCR_Y2K register, which the hardware does not refuse to do.

A subsequent probing of the clock fails due to the invalid value range in
the register, though.

[ And if it didn't, reading the clock would yield a bogus year because
  the function translating registers to tm_year is assuming a register
  value of 19 or 20. ]

This fixes the conversion from years since 1900 in tm_year to the
corresponding CCR_Y2K value of 19 or 20.
Signed-off-by: NJohannes Weiner <jw@emlix.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Paul Gortmaker <p_gortmaker@yahoo.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-x1205.c

@@ -195,7 +195,7 @@ static int x1205_set_datetime(struct i2c_client *client, struct rtc_time *tm,
 		/* year, since the rtc epoch*/
 		buf[CCR_YEAR] = bin2bcd(tm->tm_year % 100);
 		buf[CCR_WDAY] = tm->tm_wday & 0x07;
-		buf[CCR_Y2K] = bin2bcd(tm->tm_year / 100);
+		buf[CCR_Y2K] = bin2bcd((tm->tm_year + 1900) / 100);
 	}
 
 	/* If writing alarm registers, set compare bits on registers 0-4 */