scripts/config: fix variable substitution command

Commit 229455bc02b87f7128f190c4491b4ceffff38648 accidentally changed the
separator between sed `s' command and its parameters from ':' to '/'.

Revert this change.

Reported-and-tested-by: Linus Walleij <[e-mail]>
Signed-off-by: Clement Chauplannaz <[e-mail]>
Signed-off-by: Michal Marek <[e-mail]>

scripts/config

···
 	local infile="$3"
 	local tmpfile="$infile.swp"
 
-	sed -e "s/$before/$after/" "$infile" >"$tmpfile"
+	sed -e "s:$before:$after:" "$infile" >"$tmpfile"
 	# replace original file with the edited one
 	mv "$tmpfile" "$infile"
 }