hw/arm/allwinner: Clean up local variable shadowing

hw/arm/allwinner: Clean up local variable shadowing

Fix:

  hw/arm/allwinner-r40.c:412:14: error: declaration shadows a local variable [-Werror,-Wshadow]
    for (int i = 0; i < AW_R40_NUM_MMCS; i++) {
             ^
  hw/arm/allwinner-r40.c:299:14: note: previous declaration is here
    unsigned i;
             ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-ID: <20230904161235.84651-10-philmd@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>