KVM: x86: switch kvm_set_memory_alias to SRCU update

Using a similar two-step procedure as for memslots.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2bb24a8..c680f7b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -859,7 +859,7 @@
 	int i;
 	struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
 
-	gfn = unalias_gfn(kvm, gfn);
+	gfn = unalias_gfn_instantiation(kvm, gfn);
 	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
 		struct kvm_memory_slot *memslot = &slots->memslots[i];
 
@@ -896,7 +896,7 @@
 {
 	struct kvm_memory_slot *slot;
 
-	gfn = unalias_gfn(kvm, gfn);
+	gfn = unalias_gfn_instantiation(kvm, gfn);
 	slot = gfn_to_memslot_unaliased(kvm, gfn);
 	if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
 		return bad_hva();