If an invalid trigger name is provided via sysfs currently no error
is returned. Therefore it's not possible to determine whether the
trigger was set successfully.
Fix this by returning -EINVAL if no trigger is matched.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>