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>

block/blk-settings.c

@@ -500,6 +500,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 
 	return 0;
 }
+EXPORT_SYMBOL(blk_stack_limits);
 
 /**
  * disk_stack_limits - adjust queue limits for stacked drivers