usb: xhci: refine xhci_decode_trb()

Replace 'TRB_FIELD_TO_TYPE(field3)' with 'type' to simplify
code.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>