core: Fix JSON object memory leak
core: Fix JSON object memory leak

This patch fixes the following memory leak:
==6047==    by 0x53B978A: json_object_new_object (in /usr/lib/libjson-c.so.2.0.1)
==6047==    by 0x53BBBD5: json_tokener_parse_ex (in /usr/lib/libjson-c.so.2.0.1)
==6047==    by 0x53BC536: json_tokener_parse_verbose (in /usr/lib/libjson-c.so.2.0.1)
==6047==    by 0x53BC59D: json_tokener_parse (in /usr/lib/libjson-c.so.2.0.1)
==6047==    by 0x402FF5: parse_device_info

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source