USB: serial: io_ti: fix I/O after disconnect

USB: serial: io_ti: fix I/O after disconnect

commit 2330d0a853da260d8a9834a70df448032b9ff623 upstream.

Cancel the heartbeat work on driver unbind in order to avoid I/O after
disconnect in case the port is held open.

Note that the cancel in release() is still needed to stop the heartbeat
after late probe errors.

Fixes: 26c78daade0f ("USB: io_ti: Add heartbeat to keep idle EP/416 ports from disconnecting")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>