This change drops a workaround for golang.org/issues/13372.

The compiler in Go 1.6 or above handles the "conversion of a
unsafe.Pointer to uintptr when calling syscall.Syscall" case
correctly.

Also fixes a typo.

Change-Id: I0433f3b8f75b34437aad91c6e8cf103e884d2a83
Reviewed-on: https://go-review.googlesource.com/37171Reviewed-by: Ian Lance Taylor <iant@golang.org>