fixed type error in SPIRV code generator

Bug: skia:7281
Change-Id: Icf3b4fb22292ef089aeff5f54d8ea3c54bcbc2e7
Reviewed-on: https://skia-review.googlesource.com/70103
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed