all: fix some staticcheck errors

Updates golang/go#35718

Change-Id: I10bfd5421cd44bb58b8bcaa6e9205040c25f51be
Reviewed-on: https://go-review.googlesource.com/c/tools/+/208257
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
diff --git a/internal/fastwalk/fastwalk_test.go b/internal/fastwalk/fastwalk_test.go
index a122ddf..a6d9bea 100644
--- a/internal/fastwalk/fastwalk_test.go
+++ b/internal/fastwalk/fastwalk_test.go
@@ -184,7 +184,7 @@
 				mu.Lock()
 				defer mu.Unlock()
 				want["/src/"+filepath.Base(path)] = 0
-				return fastwalk.SkipFiles
+				return fastwalk.ErrSkipFiles
 			}
 			return nil
 		},
@@ -208,7 +208,7 @@
 	},
 		func(path string, typ os.FileMode) error {
 			if typ == os.ModeSymlink {
-				return fastwalk.TraverseLink
+				return fastwalk.ErrTraverseLink
 			}
 			return nil
 		},