nvmet: fix memory leak in nvmet_subsys_attr_model_store_locked

nvmet: fix memory leak in nvmet_subsys_attr_model_store_locked

[ Upstream commit becc4cac309dc867571f0080fde4426a6c2222e0 ]

Since model_number is allocated before it needs to be freed before
kmemdump_nul.

Reviewed-by: Konstantin Shelekhin <k.shelekhin@yadro.com>
Reviewed-by: Dmitriy Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Aleksandr Miloserdov <a.miloserdov@yadro.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>