tty: always relink the port

BugLink: https://bugs.launchpad.net/bugs/1859865

commit 273f6329 upstream.

If the serial device is disconnected and reconnected, it re-enumerates
properly but does not link it. fwiw, linking means just saving the port
index, so allow it always as there is no harm in saving the same value
again even if it tries to relink with the same port.

Fixes: fb2b9001 ("tty: link tty and port before configuring it as console")
Reported-by: Kenneth R. Crudup <kenny@panix.com>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191227174434.12057-1-sudipm.mukherjee@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/tty/tty_port.c

@@ -48,8 +48,7 @@ void tty_port_link_device(struct tty_port *port,
 {
 	if (WARN_ON(index >= driver->num))
 		return;
-	if (!driver->ports[index])
-		driver->ports[index] = port;
+	driver->ports[index] = port;
 }
 EXPORT_SYMBOL_GPL(tty_port_link_device);