When running on 32 bit TCG backends a wide unaligned load ends up
truncating data before returning to the guest. We specifically have
the return type as uint64_t to avoid any premature truncation so we
should use the same for the interim types.

Fixes: https://bugs.launchpad.net/qemu/+bug/1830872


Fixes: eed56642

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>