mm, hugetlb: define page_hstate for !HUGETLB_PAGE

This is a single hunk introduced later in the upstream commit
cb900f41 (mm, hugetlb: convert
hugetlbfs to use split pmd lock). We need page_hstate even for
!HUGETLB_PAGE case for the next patch (mm: thp: give transparent
hugepage code a separate copy_page).
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

include/linux/hugetlb.h

@@ -418,6 +418,7 @@ struct hstate {};
 #define hstate_sizelog(s) NULL
 #define hstate_vma(v) NULL
 #define hstate_inode(i) NULL
+#define page_hstate(page) NULL
 #define huge_page_size(h) PAGE_SIZE
 #define huge_page_mask(h) PAGE_MASK
 #define vma_kernel_pagesize(v) PAGE_SIZE