postmarketos-base-downstream: dependencies fix.

I asked 4 months ago to @Newbyte (on the comment of the !4852 (merged) MR) about this patch of code for the GDM and LightDM fixes for the fresh installation start. I don't know if the issue still happening because it could have being resolved on other issue. If it's not the case, this can fix it. Best regards and thanks for the help.