copy_signal() cleanup: clean tty_audit_fork()

Remove unneeded initialization in tty_audit_fork().  It is called only via
copy_signal() and is useless after the kmem_cache_zalloc() was used.
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_audit.c

@@ -148,7 +148,6 @@ void tty_audit_fork(struct signal_struct *sig)
 	spin_lock_irq(&current->sighand->siglock);
 	sig->audit_tty = current->signal->audit_tty;
 	spin_unlock_irq(&current->sighand->siglock);
-	sig->tty_audit_buf = NULL;
 }
 
 /**