KVM: MMU: Fix memory leak on guest demand faults

While backporting 72dc67a6, a gfn_to_page()
call was duplicated instead of moved (due to an unrelated patch not being
present in mainline).  This caused a page reference leak, resulting in a
fairly massive memory leak.

Fix by removing the extraneous gfn_to_page() call.
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/mmu.c

@@ -1412,7 +1412,7 @@ static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	up_read(&current->mm->mmap_sem);
 
 	vcpu->arch.update_pte.gfn = gfn;
-	vcpu->arch.update_pte.page = gfn_to_page(vcpu->kvm, gfn);
+	vcpu->arch.update_pte.page = page;
 }
 
 void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,