serial: stop passing NULL to functions that expect data

Earlier patches have removed the checking for old v new differences from the
USB drivers so we can now pass in a valid blank old termios so that we don't
to fill the drivers with magic hacks for console support

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>