binding: navigation: deep copy json response for cache

To avoid possible side effects from afb framework releasing
a cached json_object just deep copy to target cached object.

Bug-AGL: SPEC-2880
Change-Id: Ie953d4668cd4e9a33a91d727a378cd24e75f112e
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>