USB: serial: quatech2: drop redundant tty_buffer_request_room

Drop redundant calls to tty_buffer_request_room and use the more
efficient tty_insert_flip_char when inserting single characters.
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/quatech2.c

@@ -601,7 +601,6 @@ static void qt2_process_read_urb(struct urb *urb)
 				escapeflag = true;
 				break;
 			case QT2_CONTROL_ESCAPE:
-				tty_buffer_request_room(&port->port, 2);
 				tty_insert_flip_string(&port->port, ch, 2);
 				i += 2;
 				escapeflag = true;
@@ -616,8 +615,7 @@ static void qt2_process_read_urb(struct urb *urb)
 				continue;
 		}
 
-		tty_buffer_request_room(&port->port, 1);
-		tty_insert_flip_string(&port->port, ch, 1);
+		tty_insert_flip_char(&port->port, *ch, TTY_NORMAL);
 	}
 
 	tty_flip_buffer_push(&port->port);