rng-tools: Fix path of default configuration file

The initscript expects the config file in the folder /etc/default/
but the recipe copied it to /etc. The recipe already created the folder
/etc/default/ put it there.

Signed-off-by: Christian Ege <k4230r6@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>