aspeed/scu: Use qemu_guest_getrandom_nofail

aspeed/scu: Use qemu_guest_getrandom_nofail

The random number is intended for use by the guest.  As such, we should
honor the -seed argument for reproducibility.  Use the *_nofail routine
instead of rolling our own error handling locally.

Reviewed-by: Laurent Vivier <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Reviewed-by: Joel Stanley <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>