poly1305: make data declared in assembly files private

Update golang/go#18673.

Change-Id: I3ba89bab42f17e6fd7005df40c7a853aef1fda37
Reviewed-on: https://go-review.googlesource.com/35259
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
2 files changed