usbserial: Reference leak

A sufficiently-large number of USB serial devices causes a reference leak
when /proc/tty/drivers/usbserial is read.

Signed-Off-By: Matthias Urlichs <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/serial/usb-serial.c

···
 		length += sprintf (page+length, " path:%s", tmp);
 			
 		length += sprintf (page+length, "\n");
-		if ((length + begin) > (off + count))
+		if ((length + begin) > (off + count)) {
+			usb_serial_put(serial);
 			goto done;
+		}
 		if ((length + begin) < off) {
 			begin += length;
 			length = 0;