memdump: fix warnings.

mm_heap/mm_malloc.c: In function 'mm_malloc':
mm_heap/mm_malloc.c:281:33: warning: excess elements in struct initializer
  281 |         MM_BACKTRACE_ALLOC_PID, 0, ULONG_MAX
      |                                 ^
mm_heap/mm_malloc.c:281:33: note: (near initialization for 'dump')
mm_heap/mm_malloc.c:281:36: warning: excess elements in struct initializer
  281 |         MM_BACKTRACE_ALLOC_PID, 0, ULONG_MAX
      |                                    ^~~~~~~~~
mm_heap/mm_malloc.c:281:36: note: (near initialization for 'dump')

Signed-off-by: hanqiyuan <hanqiyuan@xiaomi.com>

mm/mm_heap/mm_malloc.c

@@ -359,7 +359,11 @@ FAR void *mm_malloc(FAR struct mm_heap_s *heap, size_t size)
 #  ifdef CONFIG_MM_DUMP_DETAILS_ON_FAILURE
       struct mm_memdump_s dump =
       {
+#if CONFIG_MM_BACKTRACE >= 0
         PID_MM_ALLOC, 0, ULONG_MAX
+#else
+        PID_MM_ALLOC
+#endif
       };
 #  endif
 #endif