efi: drop "ret_" prefix from "ret_sections[]" parameter

efi: drop "ret_" prefix from "ret_sections[]" parameter

While we write data to this parameter, it's not really a return
parameter, we after all do not fully set it, we just fill in some
fields. Hence it must be initialized beforehand.

According to our coding style only parameters that are purely used for
returning something should be named "ret_xyz", hence this one should not
be.

(We'll later rely on the current behaviour that it leaves array entries
for which we find no sections untouched, hence leave behaviour as is,
just rename the parameters to something more appropriate).

(Since we are dropping the "ret_" prefix of "ret_sections", let's rename
the old "section" parameter at the same time to "section_names", to make
clearer what it is about).