CIFS: SMBD: _smbd_get_connection() can be static

Fixes: 07495ff5d9bc ("CIFS: SMBD: Establish SMB Direct connection")
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Acked-by: Long Li <longli@microsoft.com>