rtc-pcf8563: detect polarity of century bit automatically

rtc-pcf8563: detect polarity of century bit automatically

The usage of the century bit was inverted on 2.6.19 following to PCF8563's
description, but it was not match to usage suggested by RTC8564's
datasheet.  Anyway what MO_C=1 means can vary on each platform.  This patch
is to detect its polarity in get_datetime routine.  The default value of
c_polarity is 0 (MO_C=1 means 19xx) so that this patch does not change
current behavior even if get_datetime was not called before set_datetime.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@teamlog.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>