In SPIRVCodeGenerator, use the Program's ModifiersPool

We were passing in the IR generator's which had already been reset, so
technically belonged to the *next* Program to be compiled.

Change-Id: Ib68c283591f02d1642bb7c2d9658f5caa76b0f15
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/324700
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
5 files changed