serial: samsung: Remove useless spinlock

Spinlock taken only for dma_map_single() for TX buffer is completely
useless and doesn't protect anything, so remove it to simplify the code.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung.c

@@ -906,13 +906,9 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
 		goto err_free_rx;
 	}
 
-	spin_lock_irqsave(&p->port.lock, flags);
-
 	/* TX buffer */
 	dma->tx_addr = dma_map_single(p->port.dev, p->port.state->xmit.buf,
 				UART_XMIT_SIZE, DMA_TO_DEVICE);
-
-	spin_unlock_irqrestore(&p->port.lock, flags);
 	if (dma_mapping_error(p->port.dev, dma->tx_addr)) {
 		ret = -EIO;
 		goto err_unmap_rx;