drm/i915/gt: Mark up ips_mchdev pointer access

drivers/gpu/drm/i915/gt/intel_rps.c:1726:24: error: incompatible types in comparison expression (different address spaces):
drivers/gpu/drm/i915/gt/intel_rps.c:1726:24:    struct drm_i915_private [noderef] <asn:4> *
drivers/gpu/drm/i915/gt/intel_rps.c:1726:24:    struct drm_i915_private *
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191212140459.1307617-7-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_rps.c

@@ -1723,7 +1723,7 @@ void intel_rps_driver_register(struct intel_rps *rps)
 
 void intel_rps_driver_unregister(struct intel_rps *rps)
 {
-	if (ips_mchdev == rps_to_i915(rps))
+	if (rcu_access_pointer(ips_mchdev) == rps_to_i915(rps))
 		rcu_assign_pointer(ips_mchdev, NULL);
 }