unix: switch (*CPUSet).Zero to clear builtin

clear was added to Go 1.21 and is better than the manual loop approach.

Change-Id: I851203714446e21b6329e2bcf308f2571d339e36
GitHub-Last-Rev: 71dc7f073e50a43a11ab10d3d9ef35ebe5b183f5
GitHub-Pull-Request: golang/sys#262
Reviewed-on: https://go-review.googlesource.com/c/sys/+/698495
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Keith Randall <khr@golang.org>

unix/affinity_linux.go

@@ -38,9 +38,7 @@ func SchedSetaffinity(pid int, set *CPUSet) error {
 
 // Zero clears the set s, so that it contains no CPUs.
 func (s *CPUSet) Zero() {
-	for i := range s {
-		s[i] = 0
-	}
+	clear(s[:])
 }
 
 func cpuBitsIndex(cpu int) int {