Patch wacky_yuv_formats_imggen GM

This GM got out of whack in: https://skia-review.googlesource.com/c/skia/+/1052336.
All the raster configs would only render the topmost row and then skip all the others.

Change-Id: Ibffc617c27d0b81a66cc5696aa9a9951538d3904
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1057936
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Thomas Smith <thomsmit@google.com>