iio:meter:ade7759: Removing use of deprecated macros (S_IRUGO, S_IWUSR)

This fixes the coding style issue of using (S_IWUSR | S_IRUGO) in place of
4-digit octal numbers.
Signed-off-by: Chen Guanqiao <chen.chenchacha@foxmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/meter/ade7759.c

@@ -317,11 +317,11 @@ static IIO_DEV_ATTR_ACTIVE_POWER_GAIN(0644,
 		ade7759_read_16bit,
 		ade7759_write_16bit,
 		ADE7759_APGAIN);
-static IIO_DEV_ATTR_CH_OFF(1, S_IWUSR | S_IRUGO,
+static IIO_DEV_ATTR_CH_OFF(1, 0644,
 		ade7759_read_8bit,
 		ade7759_write_8bit,
 		ADE7759_CH1OS);
-static IIO_DEV_ATTR_CH_OFF(2, S_IWUSR | S_IRUGO,
+static IIO_DEV_ATTR_CH_OFF(2, 0644,
 		ade7759_read_8bit,
 		ade7759_write_8bit,
 		ADE7759_CH2OS);