staging: iio: replace symbolic permission

This patch fixes the following checkpatch.pl warning in ad7150.c
WARNING: Symbolic permissions 'S_IRUGO | S_IWUSR' are not preferred
Occured during build.
Signed-off-by: Amit Kushwaha <kushwaha.a@samsung.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/cdc/ad7150.c

@@ -414,7 +414,7 @@ static ssize_t ad7150_store_timeout(struct device *dev,
 
 #define AD7150_TIMEOUT(chan, type, dir, ev_type, ev_dir)		\
 	IIO_DEVICE_ATTR(in_capacitance##chan##_##type##_##dir##_timeout, \
-		S_IRUGO | S_IWUSR,					\
+		0644,							\
 		&ad7150_show_timeout,					\
 		&ad7150_store_timeout,					\
 		IIO_UNMOD_EVENT_CODE(IIO_CAPACITANCE,			\