tty: fix missing assignment

We're trying to save the termios state and we need to allocate a buffer
to do it.  Smatch complains that the buffer is leaked at the end of the
function.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>