cmd/link: fix Codeblk printing when -a to use Textp as a slice

Does anyone actually pass -a to the linker?

Change-Id: I1d31ea66aa5604b7fd42adf15bdab71e9f52d0ed
Reviewed-on: https://go-review.googlesource.com/22356
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/link/internal/ld/data.go

@@ -798,19 +798,20 @@ func Codeblk(addr int64, size int64) {
 		return
 	}
 
-	var sym *LSym
-	for _, sym = range Ctxt.Textp {
+	syms := Ctxt.Textp
+	for i, sym := range syms {
 		if !sym.Attr.Reachable() {
 			continue
 		}
 		if sym.Value >= addr {
+			syms = syms[i:]
 			break
 		}
 	}
 
 	eaddr := addr + size
 	var q []byte
-	for ; sym != nil; sym = sym.Next {
+	for _, sym := range syms {
 		if !sym.Attr.Reachable() {
 			continue
 		}