Fixes errors in the form of:
/Users/user/src/openwrt/openwrt/build_dir/hostpkg/json-c-0.16/json_util.c:63:35: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
const char *json_util_get_last_err()
^
void
1 error generated.
ninja: build stopped: subcommand failed.
Reported-by: Paul Spooren <mail@aparcar.org>
Suggested-by: Paul Spooren <mail@aparcar.org>
Signed-off-by: Nick Hainke <vincent@systemli.org>
