!12812 serial: protect uart_port_dtr_rts() in uart_shutdown() too

Merge Pull Request from: @ci-robot 
 
PR sync from: Yi Yang <yiyang13@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/UOP7OZ3WBF4D7KS7ZBG5RUCZNRRE5FDD/ 
 
https://gitee.com/src-openeuler/kernel/issues/IAYREU 
 
Link:https://gitee.com/openeuler/kernel/pulls/12812 

Reviewed-by: Yang Yingliang <yangyingliang@huawei.com> 
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>

drivers/tty/serial/serial_core.c

@@ -286,14 +286,16 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 		/*
 		 * Turn off DTR and RTS early.
 		 */
-		if (uport && uart_console(uport) && tty) {
-			uport->cons->cflag = tty->termios.c_cflag;
-			uport->cons->ispeed = tty->termios.c_ispeed;
-			uport->cons->ospeed = tty->termios.c_ospeed;
-		}
+		if (uport) {
+			if (uart_console(uport) && tty) {
+				uport->cons->cflag = tty->termios.c_cflag;
+				uport->cons->ispeed = tty->termios.c_ispeed;
+				uport->cons->ospeed = tty->termios.c_ospeed;
+			}
 
-		if (!tty || C_HUPCL(tty))
-			uart_port_dtr_rts(uport, 0);
+			if (!tty || C_HUPCL(tty))
+				uart_port_dtr_rts(uport, 0);
+		}
 
 		uart_port_shutdown(port);
 	}