mm/pgtable: define pte_index so that preprocessor could recognize it

Since commit 974b9b2 ("mm: consolidate pte_index() and
pte_offset_*() definitions") pte_index is a static inline and there is
no define for it that can be recognized by the preprocessor.  As a
result, vm_insert_pages() uses slower loop over vm_insert_page() instead
of insert_pages() that amortizes the cost of spinlock operations when
inserting multiple pages.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 974b9b2 ("mm: consolidate pte_index() and pte_offset_*() definitions")
Signed-off-by: Mike Rapoport <[email protected]>
Reported-by: Christian Dietrich <[email protected]>
Reviewed-by: Khalid Aziz <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/pgtable.h

@@ -62,6 +62,7 @@ static inline unsigned long pte_index(unsigned long address)
 {
 	return (address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
 }
+#define pte_index pte_index
 
 #ifndef pmd_index
 static inline unsigned long pmd_index(unsigned long address)