drivers/rtc/rtc-vt8500.c: correct handling of CR_24H bitfield

Control register bitfield for 12H/24H mode is handled incorrectly.
Setting CR_24H actually enables 12H mode.  This patch renames the define
and changes the initialization code to correctly set 24H mode.

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