KVM: x86: Check the right feature bit for MSR_KVM_ASYNC_PF_ACK access

MSR_KVM_ASYNC_PF_ACK MSR is part of interrupt based asynchronous page fault
interface and not the original (deprecated) KVM_FEATURE_ASYNC_PF. This is
stated in Documentation/virt/kvm/msr.rst.

Fixes: 66570e96 ("kvm: x86: only provide PV features if enabled in guest's CPUID")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Message-Id: <20210722123018.260035-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>