KVM: Use page_private()/set_page_private() apis

Besides using an established api, this allows using kvm in older kernels.

Signed-off-by: Markus Rechberger <markus.rechberger@amd.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm.h

@@ -523,7 +523,7 @@ static inline struct kvm_mmu_page *page_header(hpa_t shadow_page)
 {
 	struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
 
-	return (struct kvm_mmu_page *)page->private;
+	return (struct kvm_mmu_page *)page_private(page);
 }
 
 static inline u16 read_fs(void)