thermal: rcar_thermal: Use usleep_range() instead of udelay()

rcar_thermal_update_temp() takes a mutex, so it is always called in a
context that can sleep.  Hence replace the 300 µs busy loop by a call to
usleep_range(), to allow other threads to run.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200115125417.5263-1-geert+renesas@glider.be

drivers/thermal/rcar_thermal.c

@@ -219,7 +219,7 @@ static int rcar_thermal_update_temp(struct rcar_thermal_priv *priv)
 		 * to get stable temperature.
 		 * see "Usage Notes" on datasheet
 		 */
-		udelay(300);
+		usleep_range(300, 400);
 
 		new = rcar_thermal_read(priv, THSSR) & CTEMP;
 		if (new == old) {