control/controlclient: add missing word in comment

Found by review.ai.

Updates #cleanup

Change-Id: Ib9126de7327527b8b3818d92cc774bb1c7b6f974
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlclient/auto.go

@@ -625,7 +625,7 @@ func (c *Auto) sendStatus(who string, err error, url string, nm *netmap.NetworkM
 		// We CAS here because the caller goroutine is
 		// doing a Store which we want to want to win
 		// a race. This is only a memory optimization
-		// and is for correctness:
+		// and is not for correctness:
 		c.lastStatus.CompareAndSwap(newSt, nil)
 	})
 }