Add stub for IoOpenDeviceRegistryKey

[Paul Chitescu]

+    FIXME( "stub:\n");
+    return STATUS_SUCCESS;

This is incorrect, since you are adding a stub you must not return success as 
it would imply that *DevInstRegKey is filled with a valid handle.

You must either return an error or provide a full valid implementation 
(unlikely). Anything else is your private hack, unsuitable for including in 
the public wine repository since it could crash some drivers.