zboot: Correct use of state_mask argument

There is confusion in this function between the flag and state_mask
parameters, which prevents the boot from actually happening. Correct
this by using state_mask instead of flag for deciding which states to go
through.

This fixes booting of some 32-bit Debian kernels.

Note: Some sort of CI for this is in the works.

Fixes: 228c6722 ("x86: zboot: Avoid iteration in do_zboot_states()")

Signed-off-by: Simon Glass <sjg@chromium.org>