sh: kprobes: Default to NOTIFY_DONE for unhandled debug traps.

Presently this is doing a force_sig() SIGTRAP, which is already taken
care of in the generic code if no one asserts NOTIFY_STOP. Switch the
default return to NOTIFY_DONE in the case of unhandled traps, so that
the same trap may pass through to other users on the same die chain.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>