ntb_hw_switchtec: Make function switchtec_ntb_remove() static

Fixes the following sparse warnings:

drivers/ntb/hw/mscc/ntb_hw_switchtec.c:1552:6: warning:
 symbol 'switchtec_ntb_remove' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: NLogan Gunthorpe <logang@deltatee.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>

drivers/ntb/hw/mscc/ntb_hw_switchtec.c

@@ -1549,7 +1549,7 @@ static int switchtec_ntb_add(struct device *dev,
 	return rc;
 }
 
-void switchtec_ntb_remove(struct device *dev,
+static void switchtec_ntb_remove(struct device *dev,
 				 struct class_interface *class_intf)
 {
 	struct switchtec_dev *stdev = to_stdev(dev);