USB: serial: ti_usb_3410_5052: fix array underflow in completion handler

Similarly to a recently reported bug in io_ti, a malicious USB device could set port_number to -3 and we would underflow the port array in the interrupt completion handler.

As these devices only have one or two ports, fix this by making sure we only consider the seventh bit when determining the port number (and ignore bits 0xb0 which are typically set to 0x30).

---
 drivers/usb/serial/ti_usb_3410_5052.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 3010878f7f8e..e3c5832337e0 100644
@@ -1119,7 +1119,7 @@ static void ti_break(struct tty_struct *tty, int break_state)
 
 static int ti_get_port_from_code(unsigned char code)
 {
-	return (code >> 4) - 3;
+	return (code >> 6) & 0x01;
 }
 
 static int ti_get_func_from_code(unsigned char code)