openrisc: add missing pgtable_page_ctor/dtor calls

It will fix NR_PAGETABLE accounting. It's also required if the arch is
going ever support split ptl.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Cc: Jonas Bonn <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/openrisc/include/asm/pgalloc.h

···
 {
 	struct page *pte;
 	pte = alloc_pages(GFP_KERNEL|__GFP_REPEAT, 0);
-	if (pte)
-		clear_page(page_address(pte));
+	if (!pte)
+		return NULL;
+	clear_page(page_address(pte));
+	if (!pgtable_page_ctor(pte)) {
+		__free_page(pte);
+		return NULL;
+	}
 	return pte;
 }
 
···
 
 static inline void pte_free(struct mm_struct *mm, struct page *pte)
 {
+	pgtable_page_dtor(pte);
 	__free_page(pte);
 }