[SeaBIOS] VM won't start since 76e58028d28e78431f9de3cee0b3c88d807fa39d

[Michael S. Tsirkin]

With seabios built from source, and latest qemu, VMs hang during boot
for me.  Bisect points at this commit:
76e58028d28e78431f9de3cee0b3c88d807fa39d

Reverting this helps. Guest is stuck quite late, after
'switching root' message, so this could be just an OS
visible change that it can't handle.
Didn't try debugging more yet.