tty: serial: stm32-usart: Remove set but unused 'cookie' variables

Fixes the following W=1 kernel build warning(s):

 drivers/tty/serial/stm32-usart.c: In function ‘stm32_transmit_chars_dma’:
 drivers/tty/serial/stm32-usart.c:353:15: warning: variable ‘cookie’ set but not used [-Wunused-but-set-variable]
 drivers/tty/serial/stm32-usart.c: In function ‘stm32_of_dma_rx_probe’:
 drivers/tty/serial/stm32-usart.c:1090:15: warning: variable ‘cookie’ set but not used [-Wunused-but-set-variable]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Gerald Baeza <gerald.baeza@st.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104193549.4026187-29-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -350,7 +350,6 @@ static void stm32_transmit_chars_dma(struct uart_port *port)
 	struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
 	struct circ_buf *xmit = &port->state->xmit;
 	struct dma_async_tx_descriptor *desc = NULL;
-	dma_cookie_t cookie;
 	unsigned int count, i;
 
 	if (stm32port->tx_dma_busy)
@@ -394,7 +393,7 @@ static void stm32_transmit_chars_dma(struct uart_port *port)
 	desc->callback_param = port;
 
 	/* Push current DMA TX transaction in the pending queue */
-	cookie = dmaengine_submit(desc);
+	dmaengine_submit(desc);
 
 	/* Issue pending DMA TX requests */
 	dma_async_issue_pending(stm32port->tx_ch);
@@ -1087,7 +1086,6 @@ static int stm32_of_dma_rx_probe(struct stm32_port *stm32port,
 	struct device *dev = &pdev->dev;
 	struct dma_slave_config config;
 	struct dma_async_tx_descriptor *desc = NULL;
-	dma_cookie_t cookie;
 	int ret;
 
 	/* Request DMA RX channel */
@@ -1132,7 +1130,7 @@ static int stm32_of_dma_rx_probe(struct stm32_port *stm32port,
 	desc->callback_param = NULL;
 
 	/* Push current DMA transaction in the pending queue */
-	cookie = dmaengine_submit(desc);
+	dmaengine_submit(desc);
 
 	/* Issue pending DMA requests */
 	dma_async_issue_pending(stm32port->rx_ch);