UHCI: improved debugging checks for the frame list

This patch (as768) improves the debugging checks for the uhci-hcd
frame list.  The number of entries displayed is limited to 10, and the
driver now checks for the correct Skeleton QH link value at the end of
each chain of Isochronous TDs.  The code to compute these link values
is now used in two spots, so it is moved into its own separate
subroutine.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>