iio: magnetometer: mmc35240: Use a smaller sleep value

According to datasheet, Page 8, minimum wait time to complete
measurement is 10ms. Adjusting this value will increase the
userspace polling rate.

Fixes: abeb6b1e7b ("iio: magnetometer: Add support for MEMSIC MMC35240")
Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/magnetometer/mmc35240.c

@@ -219,7 +219,8 @@ static int mmc35240_take_measurement(struct mmc35240_data *data)
 			return ret;
 		if (reg_status & MMC35240_STATUS_MEAS_DONE_BIT)
 			break;
-		msleep(20);
+		/* minimum wait time to complete measurement is 10 ms */
+		usleep_range(10000, 11000);
 	}
 
 	if (tries < 0) {