hwmon: (pmbus) Initialize sysfs attributes

Initialize sysfs attrs before device_create_file() call to suppress
lockdep_init_map() warning:

WARNING: at kernel/lockdep.c:2701 lockdep_init_map+0x12d/0x140()
Reviewed-by: Robert Coulson <robert.coulson@ericsson.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: stable@kernel.org # .39.x

drivers/hwmon/pmbus_core.c

@@ -707,6 +707,7 @@ do {									\
 	struct sensor_device_attribute *a				\
 	    = &data->_type##s[data->num_##_type##s].attribute;		\
 	BUG_ON(data->num_attributes >= data->max_attributes);		\
+	sysfs_attr_init(&a->dev_attr.attr);				\
 	a->dev_attr.attr.name = _name;					\
 	a->dev_attr.attr.mode = _mode;					\
 	a->dev_attr.show = _show;					\