rename kStride N

This is a no-op refactor to make SkJumper_stages.cpp and
SkJumper_stages_lowp.cpp more similar.

Change-Id: Icb5dd415d105fbdc58ce0b9b63058c0a66ed4a13
Reviewed-on: https://skia-review.googlesource.com/52000
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed