nvme-cli: id-ctrl: Fix memory leak for JSON.

nvme-cli: id-ctrl: Fix memory leak for JSON.

This patch fixes the following memory leak when id-ctrl command
executed with JSON option:-
==7680==
==7680== HEAP SUMMARY:
==7680==     in use at exit: 9,796 bytes in 338 blocks
==7680==   total heap usage: 474 allocs, 136 frees, 24,729 bytes allocated
==7680==
==7680== LEAK SUMMARY:
==7680==    definitely lost: 24 bytes in 1 blocks
==7680==    indirectly lost: 9,772 bytes in 337 blocks
==7680==      possibly lost: 0 bytes in 0 blocks
==7680==    still reachable: 0 bytes in 0 blocks
==7680==         suppressed: 0 bytes in 0 blocks

Fix:-
==7971==
==7971== HEAP SUMMARY:
==7971==     in use at exit: 0 bytes in 0 blocks
==7971==   total heap usage: 474 allocs, 474 frees, 24,729 bytes allocated
==7971==

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@hgst.com>