hw/nvme: fix missing endian conversions for doorbell buffers

hw/nvme: fix missing endian conversions for doorbell buffers

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

Fixes: 3f7fe8de3d49 ("hw/nvme: Implement shadow doorbell buffer support")
Cc: qemu-stable@nongnu.org
Reported-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit 2fda0726e5149e032acfa5fe442db56cd6433c4c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Conflicts: hw/nvme/ctrl.c