cmd/go/internal/vgo: fix redundant code

Eliminate a redundant err variable in func downloadZip.

Change-Id: I0bba7b37118f6ec2ccccf23ef1de8bbadf0cd815
Reviewed-on: https://go-review.googlesource.com/106135
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

vendor/cmd/go/internal/vgo/fetch.go

diff --git a/vendor/cmd/go/internal/vgo/fetch.go b/vendor/cmd/go/internal/vgo/fetch.go
index 30ad8f7..c28353c 100644
--- a/vendor/cmd/go/internal/vgo/fetch.go
+++ b/vendor/cmd/go/internal/vgo/fetch.go
@@ -110,10 +110,7 @@
 	if err := w.Close(); err != nil {
 		return err
 	}
-	if err := ioutil.WriteFile(target+"hash", []byte(hash), 0666); err != nil {
-		return err
-	}
-	return nil
+	return ioutil.WriteFile(target+"hash", []byte(hash), 0666)
 }
 
 var useModHash = false