drivers: serial: fix uart_sam0 async rx timeout calculation

Zephyr moved to microseconds to represent uart async timeout.
This one has some additional logic that was not adjusted in
the transition from milliseconds.

c590b35 was integrated in
#39041

Signed-off-by: Stefan Giroux <stefan.g@feniex.com>

Author: sgfeniex

drivers/serial/uart_sam0.c

@@ -361,7 +361,7 @@ static void uart_sam0_rx_timeout(struct k_work *work)
 		return;
 	}
 
-	uint32_t now = k_uptime_get_32();
+	uint32_t now = USEC_PER_MSEC * k_uptime_get_32();
 	uint32_t elapsed = now - dev_data->rx_timeout_start;
 
 	if (elapsed >= dev_data->rx_timeout_time) {
@@ -762,7 +762,7 @@ static void uart_sam0_isr(const struct device *dev)
 		 */
 		if (dev_data->rx_timeout_time != SYS_FOREVER_US) {
 			dev_data->rx_timeout_from_isr = true;
-			dev_data->rx_timeout_start = k_uptime_get_32();
+			dev_data->rx_timeout_start = USEC_PER_MSEC * k_uptime_get_32();
 			k_work_reschedule(&dev_data->rx_timeout_work,
 					      K_USEC(dev_data->rx_timeout_chunk));
 		}