iio: Don't compare boolean values to true/false

Fixes the following warnings from coccicheck:
	drivers/iio/inkern.c:81:6-14: WARNING: Comparison to bool
	drivers/iio/dac/ad5686.c:191:5-11: WARNING: Comparison to bool

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/dac/ad5686.c b/drivers/iio/dac/ad5686.c
index 6948d75..bc92ff9 100644
--- a/drivers/iio/dac/ad5686.c
+++ b/drivers/iio/dac/ad5686.c
@@ -188,7 +188,7 @@
 	if (ret)
 		return ret;
 
-	if (readin == true)
+	if (readin)
 		st->pwr_down_mask |= (0x3 << (chan->channel * 2));
 	else
 		st->pwr_down_mask &= ~(0x3 << (chan->channel * 2));