leds: apu: add pr_fmt prefix for better log output

Define pr_fmt() macro for prefixing the module name to all
pr_*() outputs, in order to increase log message clarity.

Signed-off-by: Enrico Weigelt <info@metux.net>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>