don't allocate an interpreter register for stores

Instructions only need a register if they've got an output.
This more closely mirrors what the JIT does.

Change-Id: I9cddba124a90c3afa698d82b1bb89808a7abd3c6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253762
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed