hwmon: (sparx5) Fix initial reading of temperature

If the temperature is read before the internal calibration is
completed, the driver returns -EIO. Instead it should return -EAGAIN
to encourage repeating the operation.

Note (groeck): Returning -EAGAIN to userspace may result in hard loops;
some userspace code interprets -EAGAIN as request to retry immediately.
I would prefer -ENODATA, but it turns out that the thermal subsystem only
handles -EAGAIN silently, so we'll have to stick with that.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Link: https://lore.kernel.org/r/20200903134704.8949-1-lars.povlsen@microchip.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/sparx5-temp.c

@@ -56,7 +56,7 @@ static int s5_read(struct device *dev, enum hwmon_sensor_types type,
 	case hwmon_temp_input:
 		stat = readl_relaxed(hwmon->base + TEMP_STAT);
 		if (!(stat & TEMP_STAT_VALID))
-			return -EIO;
+			return -EAGAIN;
 		value = stat & TEMP_STAT_TEMP;
 		/*
 		 * From register documentation: