usb: xhci: adjust empty TD list handling in handle_tx_event()

usb: xhci: adjust empty TD list handling in handle_tx_event()

Introduce an initial check for an empty list prior to entering the while
loop. Which enables, the implementation of distinct warnings to
differentiate between scenarios where the list is initially empty and
when it has been emptied during processing skipped isoc TDs.

These adjustments not only simplifies the large while loop, but also
facilitates future enhancements to the handle_tx_event() function.

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/20240905143300.1959279-11-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>