virStorageSourceParseBackingJSON: Move deflattening of json: URIs out of recursion
Originally virStorageSourceParseBackingJSON didn't recurse, but when
the 'raw' driver support was added we need to parse it's information
which contains nested 'file' object.
Since the deflattening helper recurses already there's no need to call
it again. Move it one level up to the entry point.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>