internal/syscall/unix: fix fchownat linkname for AIX & Solaris

Typo fix: libc_chownat => libc_fchownat

Change-Id: I6721a988c19e3438b967a73559159c948ed51a0e
Reviewed-on: https://go-review.googlesource.com/c/go/+/649636
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/internal/syscall/unix/at_libc.go

@@ -17,7 +17,7 @@ import (
 //go:linkname procReadlinkat libc_readlinkat
 //go:linkname procMkdirat libc_mkdirat
 //go:linkname procFchmodat libc_fchmodat
-//go:linkname procFchownat libc_chownat
+//go:linkname procFchownat libc_fchownat
 
 var (
 	procFstatat,