KVM: x86/mmu: Use yield-safe TDP MMU root iter in MMU notifier unmapping

Use the yield-safe variant of the TDP MMU iterator when handling an
unmapping event from the MMU notifier, as most occurences of the event
allow yielding.

Fixes: e1eed584 ("KVM: x86/mmu: Allow yielding during MMU notifier unmap/zap, if possible")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211120015008.3780032-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>