isdn/gigaset: fix NULL-deref at probe

Make sure to check the number of endpoints to avoid dereferencing a
NULL-pointer should a malicious device lack endpoints.

Fixes: cf7776dc ("[PATCH] isdn4linux: Siemens Gigaset drivers -
direct USB connection")
Cc: stable <stable@vger.kernel.org>	# 2.6.17
Cc: Hansjoerg Lipp <hjlipp@web.de>
Signed-off-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/bas-gigaset.c

@@ -2317,6 +2317,9 @@ static int gigaset_probe(struct usb_interface *interface,
 		return -ENODEV;
 	}
 
+	if (hostif->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
 	dev_info(&udev->dev,
 		 "%s: Device matched (Vendor: 0x%x, Product: 0x%x)\n",
 		 __func__, le16_to_cpu(udev->descriptor.idVendor),