hw/loader: Clean up global variable shadowing in rom_add_file()

hw/loader: Clean up global variable shadowing in rom_add_file()

Fix:

  hw/core/loader.c:1073:27: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
                       bool option_rom, MemoryRegion *mr,
                            ^
  include/sysemu/sysemu.h:57:22: note: previous declaration is here
  extern QEMUOptionRom option_rom[MAX_OPTION_ROMS];
                       ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Ani Sinha <anisinha@redhat.com>
Message-Id: <20231010115048.11856-3-philmd@linaro.org>