scripts/config: fix double-quotes un-escaping

When reporting a string value, only the first double-quote was
un-escaped. We need to un-escape all escaped double-quotes.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>