hw/nvme: fix buffer overrun in nvme_changed_nslist (CVE-2021-3947)

hw/nvme: fix buffer overrun in nvme_changed_nslist (CVE-2021-3947)

Fix missing offset verification.

Cc: qemu-stable@nongnu.org
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Fixes: f432fdfa121 ("support changed namespace asynchronous event")
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit e2c57529c9306e4c9aac75d9879f6e7699584a22)
Signed-off-by: Michael Roth <michael.roth@amd.com>