The eventidx and doorbell value are not handling endianness correctly.
Fix this.

Fixes: 3f7fe8de ("hw/nvme: Implement shadow doorbell buffer support")
Cc: qemu-stable@nongnu.org
Reported-by: NGuenter Roeck <linux@roeck-us.net>
Reviewed-by: NKeith Busch <kbusch@kernel.org>
Signed-off-by: NKlaus Jensen <k.jensen@samsung.com>