ucc_geth: Fix endless loop in stop_{tx,rx} routines

Currently the routines wait for the various bits w/o an assumption that
bits may never get set. When timeouts happen I see that these bits never
get set and so the routines hang the kernel.

With this patch we'll wait the graceful stop for 100 ms, and then will
simply exit. There is nothing* we can do about that, but it's OK since
we'll do full reset later.

* Well, actually, there is also not-graceful variant for the TX stop,
  but specs says that we never should use it.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>