hw/nvme: fix endianness issue for shadow doorbells

hw/nvme: fix endianness issue for shadow doorbells

In commit 2fda0726e514 ("hw/nvme: fix missing endian conversions for
doorbell buffers"), we fixed shadow doorbells for big-endian guests
running on little endian hosts. But I did not fix little-endian guests
on big-endian hosts. Fix this.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1765
Fixes: 3f7fe8de3d49 ("hw/nvme: Implement shadow doorbell buffer support")
Cc: qemu-stable@nongnu.org
Reported-by: Thomas Huth <thuth@redhat.com>
Tested-by: Cédric Le Goater <clg@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>