google/panther: Fix RW ramstage index

google/panther: Fix RW ramstage index

Without this patch coreboot will always use the read-only version
of ramstage, even if there is a read-write version available.

BRANCH=panther
BUG=chrome-os-partner:25870
TEST=Install different RO and RW version, check in cbmem log that
     coreboot's romstage and ramstage have different timestamps
     in their banners.

Change-Id: I723a3d4479d59534660728d891a9f40a077b4ef0
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/186664
Commit-Queue: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/6005
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>