pwm: Set class for exported channels in sysfs

Notifications for devices without bus or class set get dropped by
dev_uevent_filter(). Adding the class to the exported child matches
what the GPIO subsystem is doing.

With this change exporting a channel triggers a udev event, which
gives userspace a chance to fixup permissions and makes it possible
for non-root users to make use of the PWM subsystem.
Signed-off-by: Gottfried Haider <gottfried.haider@gmail.com>
CC: Thierry Reding <thierry.reding@gmail.com>
CC: H Hartley Sweeten <hsweeten@visionengravers.com>
CC: linux-pwm@vger.kernel.org
CC: linux-arm-kernel@lists.infradead.org
CC: linux-rpi-kernel@lists.infradead.org
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/sysfs.c

@@ -263,6 +263,7 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm)
 	export->pwm = pwm;
 	mutex_init(&export->lock);
 
+	export->child.class = parent->class;
 	export->child.release = pwm_export_release;
 	export->child.parent = parent;
 	export->child.devt = MKDEV(0, 0);