fix bug in store_fff_N

The test wasn't operating on enough pixels at a time for the striding of
STORE_4 (wrong)  and STORE_3 (fixed here) to make a difference.  By
running both 1 and 4 test pixels, we are now tested against regression.

I'm a little worried this sort of thing will sneak in again or already
has given the small unit test cases I've been writing.  But I guess
that's what end-to-end testing is for?

Change-Id: Ic7e6d24103f49732bdb9193b7fbd576f8dcdaa78
Reviewed-on: https://skia-review.googlesource.com/96864
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed