cmd/internal/obj/arm64: delete needless closure in for claus

A residue of the automatic translation, this closure is easily rewritten
to a simpler, smaller, and faster construct.

Discovered while analyzing #10269, which I still plan to fix.

Change-Id: I76b12290280d81880c446b4cf75da633a94482d4
Reviewed-on: https://go-review.googlesource.com/8270
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/internal/obj/arm64/obj7.go

@@ -361,7 +361,7 @@ loop:
 	if p.Mark&FOLL != 0 {
 		i = 0
 		q = p
-		for ; i < 4; (func() { i++; q = q.Link })() {
+		for ; i < 4; i, q = i+1, q.Link {
 			if q == *last || q == nil {
 				break
 			}