usb: xhci: prevent potential failure in handle_tx_event() for Transfer events without TRB

Some transfer events don't always point to a TRB, and consequently don't
have a endpoint ring. In these cases, function handle_tx_event() should
not proceed, because if 'ep->skip' is set, the pointer to the endpoint
ring is used.

To prevent a potential failure and make the code logical, return after
checking the completion code for a Transfer event without TRBs.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240429140245.3955523-11-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>