iio: adc: ad7291: Fix indentation error by adding extra spaces

Added extra spaces before statements to fix
following indentation warnings reported by checkpatch.pl.

WARNING: Statements should start on a tabstop
+           return 0;
Signed-off-by: NAnup Sharma <anupnewsmail@gmail.com>
Link: https://lore.kernel.org/r/Y9Vf4Tp8JKvy+y0u@yogaSigned-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7291.c

@@ -179,7 +179,7 @@ static unsigned int ad7291_threshold_reg(const struct iio_chan_spec *chan,
 		offset = AD7291_VOLTAGE_OFFSET;
 		break;
 	default:
-	    return 0;
+		return 0;
 	}
 
 	switch (info) {