spapr/pci: Clean up local variable shadowing in spapr_phb_realize()

Rename SysBusDevice variable to avoid this warning :

  ../hw/ppc/spapr_pci.c: In function ‘spapr_phb_realize’:
  ../hw/ppc/spapr_pci.c:1872:24: warning: declaration of ‘s’ shadows a previous local [-Wshadow=local]
   1872 |         SpaprPhbState *s;
        |                        ^
  ../hw/ppc/spapr_pci.c:1829:19: note: shadowed declaration is here
   1829 |     SysBusDevice *s = SYS_BUS_DEVICE(dev);
        |                   ^

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-ID: <20230918145850.241074-8-clg@kaod.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>