USB: ftdi_sio: fix problem when the manufacture is a NULL string

On some misconfigured ftdi_sio devices, if the manufacturer string is
NULL, the kernel will oops when the device is plugged in.  This patch
fixes the problem.
Reported-by: Wojciech M Zabolotny <W.Zabolotny@elka.pw.edu.pl>
Tested-by: Wojciech M Zabolotny <W.Zabolotny@elka.pw.edu.pl>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/ftdi_sio.c

@@ -1769,7 +1769,8 @@ static int ftdi_8u2232c_probe(struct usb_serial *serial)
 
 	dbg("%s", __func__);
 
-	if (strcmp(udev->manufacturer, "CALAO Systems") == 0)
+	if ((udev->manufacturer) &&
+	    (strcmp(udev->manufacturer, "CALAO Systems") == 0))
 		return ftdi_jtag_probe(serial);
 
 	return 0;