xhci: really enqueue zero length TRBs.

Enqueue the first TRB even if full_len is zero.
Without this "adb install <apk>" freezes the system.

Signed-off-by: Alban Browaeys <alban.browaeys@gmail.com>
Fixes: 86065c27

 ("xhci: don't rely on precalculated value of needed trbs in the enqueue loop")
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>