Since removal of the "missed interrupt detection" nobody used the result
of whether or not we signaled anybody during that invocation, so now
remove the return value.

References: 789659f4 ("drm/i915: Drop fake breadcrumb irq")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416085218.431-1-chris@chris-wilson.co.uk