chacha20poly1305: fix typos

Change-Id: Icf4ccb29e9eae0fb6fd237ca1d8785d4fd39a8d8
Reviewed-on: https://go-review.googlesource.com/34534
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed