Fix bad symbol reference

diff -r e2956856259c include/xen/gnttab.h
@@ -108,11 +108,15 @@ static inline void __gnttab_dma_unmap_pa
 {
 }
 
-static inline void gnttab_reset_grant_page(struct page *page)
-{
-	init_page_count(page);
-	reset_page_mapcount(page);
-}
+/* init_page_count() is conditionally redefined by xen/platform-compat.h, so
+ * we can't inline a call to it.
+ */
+#define gnttab_reset_grant_page(p)		\
+	do {					\
+		struct page *_page = p;	        \
+		init_page_count(_page);		\
+		reset_page_mapcount(_page);	\
+	} while (0);				\
 
 int gnttab_suspend(void);
 int gnttab_resume(void);