KVM: x86: Use u32 for holding CPUID register value in helpers

Change the intermediate CPUID output register values from "int" to "u32"
to match both hardware and the storage type in struct cpuid_reg.

No functional change intended.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>