bluetooth rfcomm tty: destroy before tty_close()

rfcomm dev could be deleted in tty_hangup, so we must not call
rfcomm_dev_del again to prevent from destroying rfcomm dev before tty
close.

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>