Very small change to the arm64 macro assembler.
This improves Preact by 0.8% on a Neoverse-N1 machine.

Change-Id: I867e73eb9b999e6f74fd54d72c6bf3f139d3b62f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3833819
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82522}