If we don't do this then calls to StorePhi() will assume the instruction belongs to the wrong block.

Bug: b/133212545
Change-Id: If8436dcc677847a86fd629d6354e437ef46ba048
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31833
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>