os: correct err check in TestChdirAndGetwd

Due to err being shadowed in the else brach, the actual err return of
fd1.Chdir() is never checked. Fix it by not shadowing err anymore.

Change-Id: I9f1d52e88d8bc9a1c035960aa7af9f5224a63ab0
Reviewed-on: https://go-review.googlesource.com/80556
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/os_test.go

@@ -1239,9 +1239,9 @@ func TestChdirAndGetwd(t *testing.T) {
 			if mode == 0 {
 				err = Chdir(d)
 			} else {
-				fd1, err := Open(d)
-				if err != nil {
-					t.Errorf("Open %s: %s", d, err)
+				fd1, err1 := Open(d)
+				if err1 != nil {
+					t.Errorf("Open %s: %s", d, err1)
 					continue
 				}
 				err = fd1.Chdir()