usb: xhci: remove 'num_trbs' from struct 'xhci_td'

usb: xhci: remove 'num_trbs' from struct 'xhci_td'

Remove 'num_trbs' from 'xhci_td' as it's no longer used following the
removal of 'num_trbs_free' tracking in commit 2710f8186f88 ("xhci: Stop
unnecessary tracking of free trbs in a ring").

Tracking of 'num_trbs_free' is still performed in xhci DbC, but it does not
utilize 'num_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/20240626124835.1023046-6-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>