go/scanner: Simplify ErrorList.Sort implementation.

It functions exactly the same, but this is the more common
style for these kinds of multi-key comparison functions,
and is more regular.

Change-Id: I46630948f893bcc96c05eb3d36eb82e1d97a6fa0
Reviewed-on: https://go-review.googlesource.com/8358Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/scanner/errors.go

@@ -54,25 +54,16 @@ func (p ErrorList) Less(i, j int) bool {
 	// Note that it is not sufficient to simply compare file offsets because
 	// the offsets do not reflect modified line information (through //line
 	// comments).
-	if e.Filename < f.Filename {
-		return true
+	if e.Filename != f.Filename {
+		return e.Filename < f.Filename
 	}
-	if e.Filename == f.Filename {
-		if e.Line < f.Line {
-			return true
+	if e.Line != f.Line {
+		return e.Line < f.Line
 	}
-		if e.Line == f.Line {
-			if e.Column < f.Column {
-				return true
+	if e.Column != f.Column {
+		return e.Column < f.Column
 	}
-			if e.Column == f.Column {
-				if p[i].Msg < p[j].Msg {
-					return true
-				}
-			}
-		}
-	}
-	return false
+	return p[i].Msg < p[j].Msg
 }
 
 // Sort sorts an ErrorList. *Error entries are sorted by position,