Do not use return in ruby_block

This is not needed, and this creates the following error:

LocalJumpError
--------------
unexpected return

Cookbook Trace:
---------------
/var/chef/cache/cookbooks/ipmi/recipes/ipmi-discover.rb:66:in `from_file'

Note that there's nothing after the ruby_block anyway, so the intent of
return is still preserved.
Merge pull request #43 from vuntz/no-return-in-ruby_block

Do not use return in ruby_block