corrected indentation to not upset bitbake

I'm working with openembedded and following directions from Toradex which led me to this repository. However, this file was giving bitbake issues due to the inconsistent use of tab and space indentation. I've changed all indentation to consistently use spaces and bitbake no longer throws an error.

The error message was:

ERROR: ExpansionError during parsing ../stuff/oe-tworaz/meta-lxde/recipes-lxde/openbox/openbox_3.5.0.bb: Failure expanding variable populate_packages: IndentationError: unindent does not match any outer indentation level (<string>, line 5)