Remove sparse build warning

The recent session setup patch set
(cifs-Separate-rawntlmssp-auth-from-CIFS_SessSetup.patch)
had introduced a trivial sparse build warning.
Signed-off-by: Steve French <smfrench@gmail.com>
Cc: Sachin Prabhu <sprabhu@redhat.com>

fs/cifs/sess.c

@@ -1366,7 +1366,7 @@ sess_auth_rawntlmssp_authenticate(struct sess_data *sess_data)
 	sess_data->result = rc;
 }
 
-int select_sec(struct cifs_ses *ses, struct sess_data *sess_data)
+static int select_sec(struct cifs_ses *ses, struct sess_data *sess_data)
 {
 	int type;