hw/sparc/leon3: Fix wrong usage of DO_UPCAST macro

leon3.c currently fails to compile with some compilers when the -Wvla
option has been enabled:

 ../hw/sparc/leon3.c: In function ‘leon3_cpu_reset’:
 ../hw/sparc/leon3.c:153:5: error: ISO C90 forbids variable length array
  ‘offset_must_be_zero’ [-Werror=vla]
   153 |     ResetData *s = (ResetData *)DO_UPCAST(ResetData, info[id], info);
       |     ^~~~~~~~~
 cc1: all warnings being treated as errors

Looking at this code, the DO_UPCAST macro is indeed used in a wrong way
here: DO_UPCAST is supposed to check that the second parameter is the
first entry of the struct that the first parameter indicates, but since
we use and index into the info[] array, this of course cannot work.

The intention here was likely rather to use the container_of() macro
instead, so switch the code accordingly.

Fixes: d65aba8 ("hw/sparc/leon3: implement multiprocessor")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240221180751.190489-1-thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/sparc/leon3.c

@@ -150,7 +150,7 @@ static void leon3_cpu_reset(void *opaque)
 {
     struct CPUResetData *info = (struct CPUResetData *) opaque;
     int id = info->id;
-    ResetData *s = (ResetData *)DO_UPCAST(ResetData, info[id], info);
+    ResetData *s = container_of(info, ResetData, info[id]);
     CPUState *cpu = CPU(s->info[id].cpu);
     CPUSPARCState *env = cpu_env(cpu);