hw/ppc: Clean up local variable shadowing in _FDT helper routine

hw/ppc: Clean up local variable shadowing in _FDT helper routine

this fixes numerous warnings of this type :

  In file included from ../hw/ppc/spapr_pci.c:43:
  ../hw/ppc/spapr_pci.c: In function ‘spapr_dt_phb’:
  ../include/hw/ppc/fdt.h:18:13: warning: declaration of ‘ret’ shadows a previous local [-Wshadow=compatible-local]
     18 |         int ret = (exp);                                           \
        |             ^~~
  ../hw/ppc/spapr_pci.c:2355:5: note: in expansion of macro ‘_FDT’
   2355 |     _FDT(bus_off = fdt_add_subnode(fdt, 0, phb->dtbusname));
        |     ^~~~
  ../hw/ppc/spapr_pci.c:2311:24: note: shadowed declaration is here
   2311 |     int bus_off, i, j, ret;
        |                        ^~~

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-ID: <20230918145850.241074-2-clg@kaod.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>