r8152: Check for unplug in r8153b_ups_en() / r8153c_ups_en()

If the adapter is unplugged while we're looping in r8153b_ups_en() /
r8153c_ups_en() we could end up looping for 10 seconds (20 ms * 500
loops). Add code similar to what's done in other places in the driver
to check for unplug and bail.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>