Staging: iio: adc: Use usleep_range instead of msleep

This patch fixes following checkpatch.pl warning:

WARNING: msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.txt
Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Acked-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/adc/ad7192.c

@@ -213,7 +213,7 @@ static int ad7192_setup(struct ad7192_state *st,
 	ret = spi_write(st->sd.spi, &ones, 6);
 	if (ret < 0)
 		goto out;
-	msleep(1); /* Wait for at least 500us */
+	usleep_range(500, 1000); /* Wait for at least 500us */
 
 	/* write/read test for device presence */
 	ret = ad_sd_read_reg(&st->sd, AD7192_REG_ID, 1, &id);