log: make the name of error clearer

Change-Id: Id0398b51336cc74f2172d9b8e18cb1dcb520b9a0
GitHub-Last-Rev: b5cf80bf9d7f79eab1a398ad3c03f3b424aafdf1
GitHub-Pull-Request: golang/go#29931
Reviewed-on: https://go-review.googlesource.com/c/go/+/159537Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/log/log_test.go

@@ -61,9 +61,9 @@ func testPrint(t *testing.T, flag int, prefix string, pattern string, useFormat
 	line := buf.String()
 	line = line[0 : len(line)-1]
 	pattern = "^" + pattern + "hello 23 world$"
-	matched, err4 := regexp.MatchString(pattern, line)
-	if err4 != nil {
-		t.Fatal("pattern did not compile:", err4)
+	matched, err := regexp.MatchString(pattern, line)
+	if err != nil {
+		t.Fatal("pattern did not compile:", err)
 	}
 	if !matched {
 		t.Errorf("log output should match %q is %q", pattern, line)