USB: serial: Note mos7480 and option don't lock modem status

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/option.c b/drivers/usb/serial/option.c
index d101025..0e7eeb2 100644
--- a/drivers/usb/serial/option.c
+++ b/drivers/usb/serial/option.c
@@ -458,6 +458,7 @@
 
 	portdata = usb_get_serial_port_data(port);
 
+	/* FIXME: what locks portdata fields ? */
 	if (set & TIOCM_RTS)
 		portdata->rts_state = 1;
 	if (set & TIOCM_DTR)