Don't hold a pointer to the structure - there's no guarantees it'll still be vaild by command buffer execution time.

Fixes flakiness of the dEQP-VK.memory.pipeline_barrier.transfer_dst_storage_image.* tests

Bug: b/124729778
Change-Id: I747512b1a34c5d4d7dff227b15b08c69d07b298d
Reviewed-on: https://swiftshader-review.googlesource.com/c/25008
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>