mm: remove page_file_index

After using the offset of the swap entry as the key of the swap cache,
the page_index() becomes exactly same as page_file_index().  So the
page_file_index() is removed and the callers are changed to use
page_index() instead.

Link: http://lkml.kernel.org/r/1473270649-27229-2-git-send-email-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nfs/internal.h

@@ -681,11 +681,11 @@ unsigned int nfs_page_length(struct page *page)
 	loff_t i_size = i_size_read(page_file_mapping(page)->host);
 
 	if (i_size > 0) {
-		pgoff_t page_index = page_file_index(page);
+		pgoff_t index = page_index(page);
 		pgoff_t end_index = (i_size - 1) >> PAGE_SHIFT;
-		if (page_index < end_index)
+		if (index < end_index)
 			return PAGE_SIZE;
-		if (page_index == end_index)
+		if (index == end_index)
 			return ((i_size - 1) & ~PAGE_MASK) + 1;
 	}
 	return 0;