staging: dgrp: dgrp_tty.c: Remove the TIOCSSOFTCAR ioctl handler from dgrp driver

Remove the TIOCSSOFTCAR ioctl handler from dgrp driver and let the core tty
layer to take care of this ioctl instead.

Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>