drm/i915: Make queueing the hangcheck work inline

Since the function is a small wrapper around schedule_delayed_work(),
move it inline to remove the function call overhead for the principle
caller.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467390209-3576-4-git-send-email-chris@chris-wilson.co.uk