drivers: serial: silabs: add __maybe_unused to eusart dma callback

The callback function for the DMA is not used in the case where no DMA
properties are given in the esuart node in the device tree. It causes
a warning in the CI build.

Signed-off-by: Martin Hoff <martin.hoff@silabs.com>

Author: Martinhoff-maker

drivers/serial/uart_silabs_eusart.c

@@ -435,8 +435,8 @@ static void eusart_dma_rx_flush(struct eusart_data *data)
 	}
 }
 
-static void eusart_dma_rx_cb(const struct device *dma_dev, void *user_data, uint32_t channel,
-			     int status)
+__maybe_unused static void eusart_dma_rx_cb(const struct device *dma_dev, void *user_data,
+					    uint32_t channel, int status)
 {
 	const struct device *uart_dev = user_data;
 	struct eusart_data *data = uart_dev->data;
@@ -466,8 +466,8 @@ static void eusart_dma_rx_cb(const struct device *dma_dev, void *user_data, uint
 	}
 }
 
-static void eusart_dma_tx_cb(const struct device *dma_dev, void *user_data, uint32_t channel,
-			     int status)
+__maybe_unused static void eusart_dma_tx_cb(const struct device *dma_dev, void *user_data,
+					    uint32_t channel, int status)
 {
 	const struct device *uart_dev = user_data;
 	struct eusart_data *data = uart_dev->data;