A single RenderPass object may be used to record multiple command
buffers simultaneously. Storing the subpass index there produces
crosstalk between the command buffer recordings, and incorrect
rendering.

Bug: b/139824232
Change-Id: Ib8689a47733a991c61785d2d6332584f7a96f05d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35468
Presubmit-Ready: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>