xhci: add slot and endpoint numbers to debug messages in handle_tx_event

There's one annoyance in how xhci prints debug messages, we often
get logs with messages but it's hard to say from which device and
endpoint the message originates. Add slot_id, ep_index messages
in handle_tx_event.

Signed-off-by: Zhengjun Xing <zhengjun.xing@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>