Always zero vectors in start_pipeline().

The lowp start_pipeline() always zeros, and with floats we always zero
when compiled as part of Skia, so this just makes the offline float
consistent with the others.

It's getting confusing to think about which code zeros and which
doesn't, and it'd be nicer to be able to rely on zeros.

This should change code generation only to the start_pipelines in
the .S files.

Change-Id: I1178b83c01e609e40dc7912d8d56df8e36eb339d
Reviewed-on: https://skia-review.googlesource.com/52001
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
3 files changed