lib: Fix memory leak when the 'lpj' setting is read from dmesg.

It was failing to clean up and close the 'struct command' buffer,
because commit 94d90f03e2bbb595890b01e2a10b63e00e976691 added an
incomplete patch to use CLEANUP_CMD_CLOSE.

This fixes commit 94d90f03e2bbb595890b01e2a10b63e00e976691.