cmd/link: make rddataBufMax a const

Change-Id: I1ece7463d35efba0e8d2b1e61727dd25283ff720
Reviewed-on: https://go-review.googlesource.com/20059Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -437,10 +437,9 @@ func rdstring(f *obj.Biobuf) string {
 	return string(rdBuf[:n])
 }
 
-var (
-	rddataBuf    = make([]byte, rddataBufMax)
-	rddataBufMax = 1 << 14
-)
+const rddataBufMax = 1 << 14
+
+var rddataBuf = make([]byte, rddataBufMax)
 
 func rddata(f *obj.Biobuf) []byte {
 	var p []byte