drivers/rtc/rtc-vt8500.c: fix handling of data passed in struct rtc_time

tm_mon is 0..11, whereas vt8500 expects 1..12 for the month field,
causing invalid date errors for January, and causing the day field to
roll over incorrectly.

The century flag is only handled in vt8500_rtc_read_time, but not set in
vt8500_rtc_set_time.  This patch corrects the behaviour of the century
flag.

Signed-off-by: Edgar Toernig <froese@gmx.de>
Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>