Fix race condition when reading dmabuf fdinfo am: 804cd1b98b am: e0c5098938 am: 97c7509b69

Original change: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1649567

Change-Id: I1cacbc67097984f9099d6bb3ec2636551ab77d2e