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>