main/openrc: swclock init save file

See https://github.com/OpenRC/openrc/pull/560 for upstream fix that is awaiting review and merge. As it stands, swclock doesn't appear to be effective when the shipped init script is used.

I'm suggesting this is incorporated in to the Alpine package for now since there may be some precedence with !41101 (merged). Reasoning being that this is of a reasonable impact to those using Alpine without a RTC, such on a Raspberry Pi, and the upstream process to get this incorporated in to OpenRC may take some time.