We don't need to create a temporary variable for expressions like
`half3(x)`.
Change-Id: Ie0fa6a6dfb3d77d4372f96c676d3081f7e278852
Bug: skia:10786
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320960
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>