hw/pci: Clean up global variable shadowing of address_space_io variable

hw/pci: Clean up global variable shadowing of address_space_io variable

Fix:

  hw/pci/pci.c:504:54: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
                                         MemoryRegion *address_space_io,
                                                       ^
  hw/pci/pci.c:533:38: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
                         MemoryRegion *address_space_io,
                                       ^
  hw/pci/pci.c:543:40: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
                           MemoryRegion *address_space_io,
                                         ^
  hw/pci/pci.c:590:45: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
                                MemoryRegion *address_space_io,
                                              ^
  include/exec/address-spaces.h:35:21: note: previous declaration is here
  extern AddressSpace address_space_io;
                      ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20231010115048.11856-6-philmd@linaro.org>