KVM: x86: fix typo in __try_cmpxchg_user causing non-atomicness

This shows up as a TDP MMU leak when running nested.  Non-working cmpxchg on L0
relies makes L1 install two different shadow pages under same spte, and one of
them is leaked.

Fixes: 1c2361f6 ("KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220512101420.306759-1-mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>