Use uint4 instead if int4 in grvx test

Change-Id: Ic0a4c433d1d78592613b8a2fc10098ea74ee250e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/331368
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
1 file changed