imx-drm: ipu-dc: Use usleep_range instead of msleep

Since msleep(2) can sleep up to 20ms anyway, make this explicit by using
usleep_range(2000, 20000).

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/ipu-v3/ipu-dc.c

@@ -262,7 +262,7 @@ void ipu_dc_disable_channel(struct ipu_dc *dc)
 
 	/* Wait for DC triple buffer to empty */
 	while ((readl(priv->dc_reg + DC_STAT) & val) != val) {
-		msleep(2);
+		usleep_range(2000, 20000);
 		timeout -= 2;
 		if (timeout <= 0)
 			break;