KVM: cpuid: set struct kvm_cpuid_entry2 flags in do_cpuid_1_ent

do_cpuid_1_ent is typically called in two places by __do_cpuid_func
for CPUID functions that have subleafs.  Both places have to set
the KVM_CPUID_FLAG_SIGNIFCANT_INDEX.  Set that flag, and
KVM_CPUID_FLAG_STATEFUL_FUNC as well, directly in do_cpuid_1_ent.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>