m32r: fix potential NULL-pointer dereference

Add missing check for memory allocation fail.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/m32r/include/asm/pgalloc.h

@@ -43,6 +43,8 @@ static __inline__ pgtable_t pte_alloc_one(struct mm_struct *mm,
 {
 	struct page *pte = alloc_page(GFP_KERNEL|__GFP_ZERO);
 
+	if (!pte)
+		return NULL;
 	pgtable_page_ctor(pte);
 	return pte;
 }