When we close we must clear the extra reference we got when we read
port->tty. Setting the port tty NULL will clear the kref held by the driver
but not the one we obtained ourselves while doing the lookup.
Signed-off-by: NAlan Cox <alan@redhat.com>
Tested-by: NHelge Hafting <helge.hafting@aitel.hist.no>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>