sched: numa: Fix build error if CONFIG_NUMA_BALANCING && !CONFIG_TRANSPARENT_HUGEPAGE

Michal Hocko reported that the following build error occurs if
CONFIG_NUMA_BALANCING is set without THP support

  kernel/sched/fair.c: In function ‘task_numa_work’:
  kernel/sched/fair.c:932:55: error: call to ‘__build_bug_failed’ declared with attribute error: BUILD_BUG failed

The problem is that HPAGE_PMD_SHIFT triggers a BUILD_BUG() on
!CONFIG_TRANSPARENT_HUGEPAGE. This patch addresses the problem.
Reported-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sched/fair.c

@@ -929,7 +929,7 @@ void task_numa_work(struct callback_head *work)
 			continue;
 
 		/* Skip small VMAs. They are not likely to be of relevance */
-		if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < HPAGE_PMD_NR)
+		if (vma->vm_end - vma->vm_start < HPAGE_SIZE)
 			continue;
 
 		do {