scripts/feeds: fix preference of package install

scripts/feeds: fix preference of package install

The previous behavior prefered same feed for dependent packages as
initial package. This caused inconsitency in installation of packages.
The difference was if two feeds provide same package (different version)
there was different result if you executed install for that specific
version compared to install for package depending on it from different
feed.

This ensures that preferred feed is propagated without change and
selected feed is used only really for package it was selected for.

Signed-off-by: Karel Kočí <karel.koci@nic.cz>