simplify SkConfig8888 logic: just fall-through if memcpy case isn't supported

Will make future changes clearer: e.g. https://skia-review.googlesource.com/c/5152/

BUG=skia:

Change-Id: I7cc4dfd18bc3890153a5ca3f11f1b665658c48f7
Reviewed-on: https://skia-review.googlesource.com/5272
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
1 file changed