mISDN: Cleanup channel also if it already was deactivated

If a channel was closed after it was deactivated it could happen that
something was not proper resetted. The test if a channel is still activ
was wrong, so remove it and always do the cleanup.

Signed-off-by: Karsten Keil <kkeil@linux-pingi.de>
Signed-off-by: David S. Miller <davem@davemloft.net>