KVM: x86/mmu: Use leaf-only loop for walking TDP SPTEs when changing SPTE

Use the leaf-only TDP iterator when changing the SPTE in reaction to a
MMU notifier.  Practically speaking, this is a nop since the guts of the
loop explicitly looks for 4k SPTEs, which are always leaf SPTEs.  Switch
the iterator to match age_gfn_range() and test_age_gfn() so that a future
patch can consolidate the core iterating logic.

No real functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210326021957.1424875-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -1037,7 +1037,7 @@ static int set_tdp_spte(struct kvm *kvm, struct kvm_memory_slot *slot,
 
 	new_pfn = pte_pfn(*ptep);
 
-	tdp_root_for_each_pte(iter, root, gfn, gfn + 1) {
+	tdp_root_for_each_leaf_pte(iter, root, gfn, gfn + 1) {
 		if (iter.level != PG_LEVEL_4K)
 			continue;