Fix a mistatement in a comment

drivers/usbdev/cdcacm.c

@@ -2151,7 +2151,7 @@ static bool cdcuart_rxflowcontrol(FAR struct uart_dev_s *dev,
 {
 #ifdef CONFIG_CDCACM_IFLOWCONTROL
   /* Allocate a request */
-  /* Format the SerialControlLineState messages */
+  /* Format the SerialState notification */
   /* Submit the request on the Interrupt IN endpoint */
 #  warning Missing logic
 #endif