Now that the potential use-after-free issue is resolved we can use
devres for LED registration in this driver.

By using devres version of LED registering function we can remove the
.remove method from this driver.
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Tested-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>