percpu: use bitmap_clear

Use bitmap_clear rather than clearing individual bits in a memory region.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

mm/percpu-vm.c

@@ -184,8 +184,7 @@ static void pcpu_unmap_pages(struct pcpu_chunk *chunk,
 				   page_end - page_start);
 	}
 
-	for (i = page_start; i < page_end; i++)
-		__clear_bit(i, populated);
+	bitmap_clear(populated, page_start, page_end - page_start);
 }
 
 /**