USB keyspan_pda.c : fix problems found by CHECKER

pay attention to the return value of usb_control_msg as found by the CHECKER tool.

drivers/usb/serial/keyspan_pda.c

@@ -194,11 +194,12 @@ static void keyspan_pda_wakeup_write( struct usb_serial_port *port )
 
 static void keyspan_pda_request_unthrottle( struct usb_serial *serial )
 {
+	int result;
 
 	dbg(" request_unthrottle");
 	/* ask the device to tell us when the tx buffer becomes
 	   sufficiently empty */
-	usb_control_msg(serial->dev, 
+	result = usb_control_msg(serial->dev, 
 				 usb_sndctrlpipe(serial->dev, 0),
 				 7, /* request_unthrottle */
 				 USB_TYPE_VENDOR | USB_RECIP_INTERFACE
@@ -208,6 +209,9 @@ static void keyspan_pda_request_unthrottle( struct usb_serial *serial )
 				 NULL,
 				 0,
 				 2*HZ);
+	if (result < 0)
+		dbg("%s - error %d from usb_control_msg", 
+		    __FUNCTION__, result);
 }
 
 
@@ -334,14 +338,19 @@ static void keyspan_pda_break_ctl (struct usb_serial_port *port, int break_state
 {
 	struct usb_serial *serial = port->serial;
 	int value;
+	int result;
+
 	if (break_state == -1)
 		value = 1; /* start break */
 	else
 		value = 0; /* clear break */
-	usb_control_msg(serial->dev, usb_sndctrlpipe(serial->dev, 0),
+	result = usb_control_msg(serial->dev, usb_sndctrlpipe(serial->dev, 0),
 				4, /* set break */
 				USB_TYPE_VENDOR | USB_RECIP_INTERFACE | USB_DIR_OUT,
 				value, 0, NULL, 0, 2*HZ);
+	if (result < 0)
+		dbg("%s - error %d from usb_control_msg", 
+		    __FUNCTION__, result);
 	/* there is something funky about this.. the TCSBRK that 'cu' performs
 	   ought to translate into a break_ctl(-1),break_ctl(0) pair HZ/4
 	   seconds apart, but it feels like the break sent isn't as long as it