USB: cdc-acm: fix TIOCGSERIAL flags

The driver reports that it always uses a low-latency mode by returning
the ASYNC_LOW_LATENCY flag through TIOCGSERIAL.

Even if this behaviour could not be changed, this may have made some
sense prior to 7a9a65ce ("cdc-acm: Fix long standing abuse of
tty->low_latency") which removed the unconditional setting of the
corresponding tty low_latency flag (something which had always been
broken in itself).

Since the driver does not have a low-latency mode, let's drop the flag.
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -913,7 +913,6 @@ static int get_serial_info(struct acm *acm, struct serial_struct __user *info)
 	struct serial_struct tmp;
 
 	memset(&tmp, 0, sizeof(tmp));
-	tmp.flags = ASYNC_LOW_LATENCY;
 	tmp.xmit_fifo_size = acm->writesize;
 	tmp.baud_base = le32_to_cpu(acm->line.dwDTERate);
 	tmp.close_delay	= acm->port.close_delay / 10;