[RFC PATCH-for-7.0] hw/i386/amd_iommu: Fix maybe-uninitialized error with GCC 12

["Philippe Mathieu-Daudé" <philippe.mathieu.daude@gmail.com>]

From: Philippe Mathieu-Daudé <f4bug@amsat.org>

Initialize 'oldlevel' early to avoid on Debian/sid:

  FAILED: libqemu-x86_64-softmmu.fa.p/hw_i386_amd_iommu.c.o
  In function 'pte_get_page_mask',
      inlined from 'amdvi_page_walk' at hw/i386/amd_iommu.c:945:25,
      inlined from 'amdvi_do_translate' at hw/i386/amd_iommu.c:989:5,
      inlined from 'amdvi_translate' at hw/i386/amd_iommu.c:1038:5:
  hw/i386/amd_iommu.c:877:38: error: 'oldlevel' may be used uninitialized [-Werror=maybe-uninitialized]
    877 |     return ~((1UL << ((oldlevel * 9) + 3)) - 1);
        |                      ~~~~~~~~~~~~~~~~^~~~
  hw/i386/amd_iommu.c: In function 'amdvi_translate':
  hw/i386/amd_iommu.c:906:41: note: 'oldlevel' was declared here
    906 |     unsigned level, present, pte_perms, oldlevel;
        |                                         ^~~~~~~~
  cc1: all warnings being treated as errors

Having:

  $ gcc --version
  gcc (Debian 12-20220313-1) 12.0.1 20220314 (experimental)

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/i386/amd_iommu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 4d13d8e697..b6d299f964 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -904,6 +904,7 @@ static void amdvi_page_walk(AMDVIAddressSpace *as, uint64_t *dte,
     /* make sure the DTE has TV = 1 */
     if (pte & AMDVI_DEV_TRANSLATION_VALID) {
         level = get_pte_translation_mode(pte);
+        oldlevel = level;
         if (level >= 7) {
             trace_amdvi_mode_invalid(level, addr);
             return;
-- 
2.35.1