fuzz: Display hexadecimal value with '0x' prefix

Use memory_region_size() to get the MemoryRegion size,
and display it with the '0x' prefix.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210612195842.1595999-1-f4bug@amsat.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/fuzz/generic_fuzz.c

@@ -841,9 +841,9 @@ static void generic_pre_fuzz(QTestState *s)
 
     g_hash_table_iter_init(&iter, fuzzable_memoryregions);
     while (g_hash_table_iter_next(&iter, (gpointer)&mr, NULL)) {
-        printf("  * %s (size %lx)\n",
+        printf("  * %s (size 0x%" PRIx64 ")\n",
                object_get_canonical_path_component(&(mr->parent_obj)),
-               (uint64_t)mr->size);
+               memory_region_size(mr));
     }
 
     if (!g_hash_table_size(fuzzable_memoryregions)) {