iio: magn: ak8975: allow a delay after enabling regulators

The datasheet actually specifies that we need to wait atleast
500us after powering on the device before trying to set mode.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/magnetometer/ak8975.c

@@ -399,6 +399,12 @@ static int ak8975_power_on(const struct ak8975_data *data)
 			 "Failed to enable specified Vid supply\n");
 		return ret;
 	}
+	/*
+	 * According to the datasheet the power supply rise time i 200us
+	 * and the minimum wait time before mode setting is 100us, in
+	 * total 300 us. Add some margin and say minimum 500us here.
+	 */
+	usleep_range(500, 1000);
 	return 0;
 }