Add workaround for Gallium TexImage internalFormat for Alpha8

Bug: skia:
Change-Id: I1e243d8c58b533bcbbc446d189d76fda5c61b3fb
Reviewed-on: https://skia-review.googlesource.com/64067
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
1 file changed