leds: led-class: Fix checkpatch warning

Fixes the following checkpatch warning:
WARNING: Prefer netdev_dbg(netdev, ... then dev_dbg(dev, ... then pr_debug(...  to printk(KERN_DEBUG ...
FILE: leds/led-class.c:214:
	printk(KERN_DEBUG "Registered led device: %s\n",

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Bryan Wu <cooloney@gmail.com>