leds: leds-wm8350: Use dev_err instead of printk

Fixes the following type of checkpatch warnings:
WARNING: Prefer netdev_err(netdev, ... then dev_err(dev, ...
then pr_err(...  to printk(KERN_ERR ...

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