USB: EHCI: fix initialization bug in iso_stream_schedule()

Commit c3ee9b76 (EHCI: improved logic for isochronous scheduling)
introduced the idea of using ehci->last_iso_frame as the origin (or
base) for the circular calculations involved in modifying the
isochronous schedule.  However, the new code it added used
ehci->last_iso_frame before the value was properly initialized.  This
patch rectifies the mistake by moving the initialization lines earlier
in iso_stream_schedule().

This fixes Bugzilla #72891.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Fixes: c3ee9b76
Reported-by: Joe Bryant <tenminjoe@yahoo.com>
Tested-by: Joe Bryant <tenminjoe@yahoo.com>
Tested-by: Martin Long <martin@longhome.co.uk>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>