Followup fix for copy/paste error that ImageLayout::GeometryShaderReadOnly was using VK_PIPELINE_STAGE_VERTEX_SHADER_BIT

Bug: angleproject:4467
Change-Id: I5be7f800177c4f36a334f1cc75f876e271ca22b1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2133089Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>