CR50: fix bug in rom_flash.c debug print message

BRANCH=none
BUG=chrome-os-partner:43025
TEST=build succeeds

Change-Id: Ieecf5072f821ec65f308604f9153c938ee08620a
Signed-off-by: nagendra modadugu <ngm@google.com>
Reviewed-on: https://chromium-review.googlesource.com/351332
Commit-Ready: Nagendra Modadugu <ngm@google.com>
Tested-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Bill Richardson <wfrichar@chromium.org>