[vulkan] Fix VkInstance leak in VK_LAYER_FUCHSIA_imagepipe_swapchain

This leak causes severe problems with the angle test suite as we
can only open 256 files in fdio, and each instance requires an fd.
So the 256th test fails in an unrelated code path with EMFILE.

Test: angle_end2end_tests doesn't crash after 256 tests

Change-Id: Id0408f2ba070b394cabf382335cea4f0968bf569
1 file changed