Return error code -ENODEV rather than '0' when the indicator node can not
be found.

Fixes: a56ba8fb ("media: leds: as3645a: Add LED flash class driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>