Vulkan: Bug fix in atomic counter buffer count calculation When binding a new atomic counter buffer to a slot it is necessary to take into account the previous binding of that slot. This rectifies a bug introduced in f7b607c63c Bug: angleproject:3566 Test: angle_unittests.exe --gtest_filter=AtomicCounterBufferTest31.AtomicCounterBuffer* Change-Id: If78954d27c3345e8620294a84e839058d7dd7b9a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2388431 Commit-Queue: Mohan Maiya <m.maiya@samsung.com> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>