SkImage_Raster: Keep tmp in scope while it is in use

BUG=skia:

Change-Id: Ida1457ad7489f23804b8e4317e283c1dce0f6fc6
Reviewed-on: https://skia-review.googlesource.com/9918
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
1 file changed