block/nvme: Automatically free qemu_memalign() with QEMU_AUTO_VFREE

Since commit 4d324c0b ("introduce QEMU_AUTO_VFREE") buffers
allocated by qemu_memalign() can automatically freed when using
the QEMU_AUTO_VFREE macro. Use it to simplify a bit.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211006164931.172349-2-philmd@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>