i915: build warning in i915_hangcheck_elapsed

[Kees Cook]

9107e9d227e3b0893829baee4ac59feb874d4c23 introduced "score", and while
it's actually not possible for it to be uninitialized (given the
return values of ring_stuck()), the warning should be suppressed. It
probably just needs a "default:" added to the switch statement.

drivers/gpu/drm/i915/i915_irq.c:1943:27: warning: ‘score’ may be used
uninitialized in this function [-Wuninitialized]

-Kees

-- 
Kees Cook
Chrome OS Security