Servo: Fix clobber_ok usage.

Clobber_ok allows us to overload signals from different overlays,
i.e. a board may have certain signals other boards will not.

Currently however if a board tries to clobber a signal that does not
exist for all boards then adding of the signal fails. This change
instead only replaces the signal if it already exists and if not
just treats it as a regular new signal.

BUG=chromium:248685
TEST=Ran locally and ensured that clobbering an unexistant signal
now works.

Change-Id: I5f2763531e88253b4cb1e7843c28107648fc9704
Reviewed-on: https://gerrit.chromium.org/gerrit/61330
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Commit-Queue: Simran Basi <sbasi@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Tested-by: Simran Basi <sbasi@chromium.org>
2 files changed