drm/i915: opregion_setup: iounmap correct address

In case of an opregion signature mismatch in intel_opregion_setup(),
iounmap the correct address.
Signed-off-by: NChristoph Fritz <chf.fritz@googlemail.com>
Cc: stable@kernel.org
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_opregion.c

@@ -512,6 +512,6 @@ int intel_opregion_setup(struct drm_device *dev)
 	return 0;
 
 err_out:
-	iounmap(opregion->header);
+	iounmap(base);
 	return err;
 }