drm/i915: fix warning for unused variable

drivers/gpu/drm/i915/intel_engine_cs.c: In function ‘intel_engine_is_idle’:
drivers/gpu/drm/i915/intel_engine_cs.c:1103:27: error: unused variable ‘dev_priv’ [-Werror=unused-variable]
  struct drm_i915_private *dev_priv = engine->i915;
                           ^~~~~~~~
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1100,8 +1100,6 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
  */
 bool intel_engine_is_idle(struct intel_engine_cs *engine)
 {
-	struct drm_i915_private *dev_priv = engine->i915;
-
 	/* Any inflight/incomplete requests? */
 	if (!i915_seqno_passed(intel_engine_get_seqno(engine),
 			       intel_engine_last_submit(engine)))