nvme-core: fix a memory leak in nvme_ns_info_from_identify()

In case of error, free the nvme_id_ns structure that was allocated
by nvme_identify_ns().

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>