block: export blk_stack_limits()

DM needs to use blk_stack_limits(), so it needs to be exported.

Acked-by: Martin K. Petersen <martin.petersen@oracle.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 5649f34..8d33934 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -500,6 +500,7 @@
 
 	return 0;
 }
+EXPORT_SYMBOL(blk_stack_limits);
 
 /**
  * disk_stack_limits - adjust queue limits for stacked drivers