tty: serial: msm: fix definition of msm_stop_dma

The msm_stop_dma() is not exported from the driver, so make
it static to stop the following warning:

drivers/tty/serial/msm_serial.c:84:6: warning: symbol 'msm_stop_dma' was not declared. Should it be static?
Signed-off-by: NBen Dooks <ben.dooks@codethink.co.uk>
Acked-by: NAndy Gross <andy.gross@linaro.org>
Reviewed-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: NStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.c

@@ -250,7 +250,7 @@ static void msm_serial_set_mnd_regs(struct uart_port *port)
 static void msm_handle_tx(struct uart_port *port);
 static void msm_start_rx_dma(struct msm_port *msm_port);
 
-void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
+static void msm_stop_dma(struct uart_port *port, struct msm_dma *dma)
 {
 	struct device *dev = port->dev;
 	unsigned int mapped;