ush: ehci: initialize altnext pointers in QH

ush: ehci: initialize altnext pointers in QH

Section 4.10.2 "Advance Queue" of ehci-specification-for-usb.pdf
specifies how an EHCI controller loads a new QTD for processing if the
QH is not already marked as active. It states:

=====
If the field Bytes to Transfer is not zero and the T-bit in the Alternate
Next qTD Pointer is set to zero, then the host controller uses the
Alternate Next qTD Pointer. Otherwise, the host controller uses the Next
qTD Pointer. If Next qTD Pointer’s T-bit is set to a one, then the host
controller exits this state and uses the horizontal pointer to the next
schedule data structure.
=====

Hence, we must ensure that the alternate next QTD pointer's T-bit
(TERMINATE) is set, so the EHCI controller knows to use the next QTD
pointer.

Signed-off-by: Stephen Warren <swarren@nvidia.com>