ppc/pnv: Make PnvXScomInterface an incomplete type

PnvXScomInterface is an interface instance. It should never be
dereferenced. Drop the dummy type definition for extra safety,
which is the common practice with QOM interfaces.

While here also convert the bogus OBJECT_CHECK() to INTERFACE_CHECK().

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <157608025541.186670.1577861507610404326.stgit@bahia.lan>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/hw/ppc/pnv_xscom.h

@@ -22,13 +22,11 @@
 
 #include "qom/object.h"
 
-typedef struct PnvXScomInterface {
-    Object parent;
-} PnvXScomInterface;
+typedef struct PnvXScomInterface PnvXScomInterface;
 
 #define TYPE_PNV_XSCOM_INTERFACE "pnv-xscom-interface"
 #define PNV_XSCOM_INTERFACE(obj) \
-     OBJECT_CHECK(PnvXScomInterface, (obj), TYPE_PNV_XSCOM_INTERFACE)
+    INTERFACE_CHECK(PnvXScomInterface, (obj), TYPE_PNV_XSCOM_INTERFACE)
 #define PNV_XSCOM_INTERFACE_CLASS(klass)                \
     OBJECT_CLASS_CHECK(PnvXScomInterfaceClass, (klass), \
                        TYPE_PNV_XSCOM_INTERFACE)