Don't support GrCubicEffect if float != fp32

Otherwise the cubic math is too unstable.

Bug: skia:
Change-Id: I2c8d8d9abcae517d42dd3eddb5bf455c7c7487dd
Reviewed-on: https://skia-review.googlesource.com/121709
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed