serial: 8250_dma: terminate transfer explicitly when timeout

There is no need to terminate transfer in the __dma_rx_complete() since it's
called at the end of transfer. Special case when serial timeout occurs is
handled separately where we have to terminate transfer.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>