ppc/pnv: fix PnvChip redefinition in <hw/ppc/pnv_xscom.h>

This redefinition generates warnings on some clang compilers and older
gcc4.4.

...include/hw/ppc/pnv_xscom.h:24:24: warning: redefinition of typedef 'PnvChip' is a C11
      feature [-Wtypedef-redefinition]
typedef struct PnvChip PnvChip;
                       ^
...include/hw/ppc/pnv.h:65:3: note: previous definition is here
} PnvChip;
  ^
1 warning generated.
  CC      ppc64-softmmu/hw/ppc/pnv_xscom.o

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/hw/ppc/pnv_xscom.h

@@ -21,8 +21,6 @@
 
 #include "qom/object.h"
 
-typedef struct PnvChip PnvChip;
-
 typedef struct PnvXScomInterface {
     Object parent;
 } PnvXScomInterface;