iio: adc: tsc2046: fix a warning message in tsc2046_adc_update_scan_mode()

These variables are unsigned so the condition can't be less than zero
and the warning message will never be printed.

Fixes: 9374e8f5 ("iio: adc: add ADC driver for the TI TSC2046 controller")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YJ+ZuO43TnguY5vq@mwandaSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ti-tsc2046.c

@@ -398,7 +398,7 @@ static int tsc2046_adc_update_scan_mode(struct iio_dev *indio_dev,
 	priv->xfer.len = size;
 	priv->time_per_scan_us = size * 8 * priv->time_per_bit_ns / NSEC_PER_USEC;
 
-	if ((priv->scan_interval_us - priv->time_per_scan_us) < 0)
+	if (priv->scan_interval_us > priv->time_per_scan_us)
 		dev_warn(&priv->spi->dev, "The scan interval (%d) is less then calculated scan time (%d)\n",
 			 priv->scan_interval_us, priv->time_per_scan_us);