remove pin in SkColor4f::premul()

As prep for fusing SkPM4f into SkColor4f,
we noticed this pin.  It's usually premature to pin
when premultiplying here if the output format is wide.

We might want to replace this with pinThenPremul(),
and add a new premul() that starts fresh without a pin?

Change-Id: I0a8df58060ccab249f4df86eb88289dbf5934fb4
Reviewed-on: https://skia-review.googlesource.com/156002
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed