include/linux/hugetlb.h: make isolate_huge_page() an inline

include/linux/hugetlb.h: make isolate_huge_page() an inline

With CONFIG_HUGETLBFS=n:

  mm/migrate.c: In function `do_move_page_to_node_array':
  include/linux/hugetlb.h:140:33: warning: statement with no effect [-Wunused-value]
   #define isolate_huge_page(p, l) false
                                   ^
  mm/migrate.c:1170:4: note: in expansion of macro `isolate_huge_page'
      isolate_huge_page(page, &pagelist);

Reported-by: Borislav Petkov <[email protected]>
Tested-by: Borislav Petkov <[email protected]>
Signed-off-by: Naoya Horiguchi <[email protected]>
Acked-by: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>