[skottie] Fix image loading in Viewer

With the switch to ImageAsset, I forgot to update the default/local
resource loader.

TBR=
Change-Id: I1ab898a896162718df04094a31648bf8e876d91b
Reviewed-on: https://skia-review.googlesource.com/c/161546
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed