hwclock: fix --systohc sets clock 0.5 seconds slow

hwclock: fix --systohc sets clock 0.5 seconds slow

quote from rh150493:

	The kernel code, when setting the BIOS clock notes that the clock time
	ticks to the next second 0.5 seconds after adjusting it  (see
	linux/arch/i386/kernel/time.c).

	hwclock --systohc sets the CMOS clock at the 1 second boundry and thus
	causes the clock to be wrong by 500ms each time it is reset.  If the
	clock is set every shutdown then the clock will have a reboot-count
	related drift as well as the natural drift problems of the clock. Note
	that this also mucks up the drift calculations, of course.

Signed-off-by: Karel Zak <kzak@redhat.com>