USB: whci-hcd: provide a endpoint_reset method

Provide a endpoint_reset method to reset sequence number and current
window.  This QHead information can only be changed while the qset is
not in a schedule.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>