internal/poll: remove named return values and naked returns

Change-Id: I283f4453e5cf8b22995b3abffccae182cfbb6945
Reviewed-on: https://go-review.googlesource.com/36970
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/internal/poll/sendfile_linux.go b/src/internal/poll/sendfile_linux.go
index 0bc7529..4014e05 100644
--- a/src/internal/poll/sendfile_linux.go
+++ b/src/internal/poll/sendfile_linux.go
@@ -11,13 +11,15 @@
 const maxSendfileSize int = 4 << 20
 
 // SendFile wraps the sendfile system call.
-func SendFile(dstFD *FD, src int, remain int64) (written int64, err error) {
+func SendFile(dstFD *FD, src int, remain int64) (int64, error) {
 	if err := dstFD.writeLock(); err != nil {
 		return 0, err
 	}
 	defer dstFD.writeUnlock()
 
 	dst := int(dstFD.Sysfd)
+	var written int64
+	var err error
 	for remain > 0 {
 		n := maxSendfileSize
 		if int64(n) > remain {