simplify SkRRect serialization

simplify SkRRect serialization

I think this happens to fix the particular issue in the attached bug.
memcpy() is kind of the swiss army knife as far as strict aliasing is
concerned... you're always allowed to use it.

The generated code for writeToMemory() is unchanged, and
readFromMemory() gets a bit better looking.

BUG=skia:5105

Change-Id: Ib5bf96600f1138650c004ced2d696e9a4ba83ca7
Reviewed-on: https://skia-review.googlesource.com/11682
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>