tests/virtio-scsi: Clean up global variable shadowing

tests/virtio-scsi: Clean up global variable shadowing

Rename the (unused) 'allow' argument, following the pattern
used by the other tests in this file. This fixes:

  tests/qtest/virtio-scsi-test.c:159:61: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
  static void hotplug(void *obj, void *data, QGuestAllocator *alloc)
                                                              ^
  tests/qtest/virtio-scsi-test.c:37:25: note: previous declaration is here
  static QGuestAllocator *alloc;
                          ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-By: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20231009100251.56019-4-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>