Use rescale in async-rescale-and-read to do non-rescaling conversions.

Removes some redundand code.

Change-Id: Iea2f2e4785f669eaff21f908bcd6e490cc8ed8c3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/405497
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed