[//gpu] Fix build of ClientSI::ComputeTextureTarget() on iOS

Bug: 41494843
Change-Id: I496b4bb4d8649a9ff702e7c1308c2a5c3d4cfe28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5405620


Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: vikas soni <vikassoni@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Commit-Queue: vikas soni <vikassoni@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Auto-Submit: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280251}