This corrects a compile error due to a mismatch between function description and the assembler code that first appeared when running TryBots on the change to vendor this code. This fixes that problem and adds and minor change based on a comment in CL 195959. Change-Id: I42cbd3f75e281913f12f74850deaedf14eb21989 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/205659 Reviewed-by: Filippo Valsorda <filippo@golang.org>