drivers: serial: nrfx_uarte: Avoid 64 bit division

When converting timeout (in microseconds) to bauds use by the HW
frame timeout use less accurate conversion but one that does not
use 64 bit division. 64 bit division takes a lot of code and time
and shoud be avoided.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

Author: nordic-krch

drivers/serial/uart_nrfx_uarte.c

@@ -1846,9 +1846,13 @@ static void notify_uart_rx_rdy(const struct device *dev, size_t len)
 #ifdef UARTE_HAS_FRAME_TIMEOUT
 static uint32_t us_to_bauds(uint32_t baudrate, int32_t timeout)
 {
-	uint64_t bauds = (uint64_t)baudrate * timeout / 1000000;
+	/* Divide baudrate by 1000 to avoid 64 bit division. This approach is not 100% accurate
+	 * but error is insignificant (within few bauds). Precise timeout my be more important
+	 * for higher baudrates but inaccuracy diminishes with higher baudrate.
+	 */
+	uint32_t bauds = ((baudrate / 1000) * timeout) / 1000;
 
-	return MIN((uint32_t)bauds, UARTE_FRAMETIMEOUT_COUNTERTOP_Msk);
+	return MIN(bauds, UARTE_FRAMETIMEOUT_COUNTERTOP_Msk);
 }
 #endif