USB: remove iteration limit in hub_tt_work()

This patch (as1621) removes the limit on the number of loops allowed
in hub_tt_work().  The value is arbitrary, and it's silly to have a
limit in the first place -- anything beyond the limit would not get
handled.

Besides, it's most unlikely that we'll ever need to clear more than a
couple of TT buffers at any time.

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