HelloStereo Sample is upside down when using vulkan

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**Describe the bug**
The hellostereo sample is upside down when running with vulkan.

**To Reproduce**
Steps to reproduce the behavior:
Build filament with multiview
Run the hellostereo sample with ./out/cmake-debug/samples/hellostereo -a vulkan

**Expected behavior**
When working properly, the two heads in the top left and right corners should be right side up and rotating.

**Screenshots**

**Logs**
N/A

**Desktop (please complete the following information):**
- OS: Linux
- GPU
- Backend: Vulkan

**Smartphone (please complete the following information):**
N/A

**Additional context**
N/A