runtime: use Go function signatures for memclr and memmove comments

runtime: use Go function signatures for memclr and memmove comments

The function signatures in the comments used a C-like style. Using
Go function signatures is cleaner.

Change-Id: I1a093ed8fe5df59f3697c613cf3fce58bba4f5c1
Reviewed-on: https://go-review.googlesource.com/113876
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>