xhci: use boolean to indicate last trb in td remainder calculation

We only need to know if we are queuing the last trb for a TD when
calculating the td remainder field.
The total number of trbs left is not used.

We won't be able to trust the pre-calculated number of trbs used if we
need to align trb data by splitting or merging trbs in order to satisfy
comply with data alignment requirements in xhci specs section 4.11.7.1.

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