serial: protect uart_port_dtr_rts() in uart_shutdown() too

Commit af224ca2 (serial: core: Prevent unsafe uart port access, part
3) added few uport == NULL checks. It added one to uart_shutdown(), so
the commit assumes, uport can be NULL in there. But right after that
protection, there is an unprotected "uart_port_dtr_rts(uport, false);"
call. That is invoked only if HUPCL is set, so I assume that is the
reason why we do not see lots of these reports.

Or it cannot be NULL at this point at all for some reason :P.

Until the above is investigated, stay on the safe side and move this
dereference to the if too.

I got this inconsistency from Coverity under CID 1585130. Thanks.
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240805102046.307511-3-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -407,7 +407,8 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 		/*
 		 * Turn off DTR and RTS early.
 		 */
-		if (uport && uart_console(uport) && tty) {
+		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;
@@ -415,6 +416,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 
 			if (!tty || C_HUPCL(tty))
 				uart_port_dtr_rts(uport, false);
+		}
 
 		uart_port_shutdown(port);
 	}