cmd/compile: use the correct const when flagging indirect map elem types

Currently both MapMaxKeyBytes and MapMaxElemBytes are 128 so there's no
functional change.

Change-Id: If687739104717ac5d0d7210fb64ae5e50b80ea95
GitHub-Last-Rev: fb099ebc0e
GitHub-Pull-Request: golang/go#77979
Reviewed-on: https://go-review.googlesource.com/c/go/+/752240
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/reflectdata/map.go

@@ -295,7 +295,7 @@ func writeMapType(t *types.Type, lsym *obj.LSym, c rttype.Cursor) {
 	if t.Key().Size() > abi.MapMaxKeyBytes {
 		flags |= abi.MapIndirectKey
 	}
-	if t.Elem().Size() > abi.MapMaxKeyBytes {
+	if t.Elem().Size() > abi.MapMaxElemBytes {
 		flags |= abi.MapIndirectElem
 	}
 	c.Field("Flags").WriteUint32(flags)