Avoid unnecessary load-store for out params in SPIR-V.

We don't need to initialize input values for `out` params. (We were
treating them the same as `inout`.)

Change-Id: Ib447d15de237a6a03740ad012180691dc60a50bd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/446717
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
3 files changed