watchdog: Fix non-standard prototype of get_softlockup_thresh()

This build warning slipped through:

  kernel/watchdog.c:102: warning: function declaration isn't a prototype

As reported by Stephen Rothwell.

Also address an unused variable warning that GCC 4.6.0 reports:
we cannot do anything about failed watchdog ops during CPU hotplug
(it's not serious enough to return an error from the notifier),
so ignore them.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Mandeep Singh Baines <msb@chromium.org>
Cc: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20110524134129.8da27016.sfr@canb.auug.org.au


Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <20110517071642.GF22305@elte.hu>