USB: oti6858: fix TCFLSH ioctl handling

Removes unimplemented TCFLSH handling from oti6858, because it was 
preventing TCFLSH handling by upper layer (line discipline) drivers (see 
drivers/char/tty_io.c line 3450).
Signed-off-by: Paulius Zaleckas <paulius.zaleckas@teltonika.lt>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/oti6858.c

@@ -814,10 +814,6 @@ static int oti6858_ioctl(struct usb_serial_port *port, struct file *file,
 				__FUNCTION__, port->number, cmd, arg);
 
 	switch (cmd) {
-		case TCFLSH:
-			/* FIXME */
-			return 0;
-
 		case TIOCMBIS:
 			if (copy_from_user(&x, user_arg, sizeof(x)))
 				return -EFAULT;