r8152: Rename RTL8152_UNPLUG to RTL8152_INACCESSIBLE

Whenever the RTL8152_UNPLUG is set that just tells the driver that all
accesses will fail and we should just immediately bail. A future patch
will use this same concept at a time when the driver hasn't actually
been unplugged but is about to be reset. Rename the flag in
preparation for the future patch.

This is a no-op change and just a search and replace.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>