platform/x86: dell-wmi-led: fix coding style issues

Fix coding style issues in dell-wmi-led to make sure the module gets a
clean start in the x86 platform driver subsystem.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>