kernel/auditfilter.c: fix leak in audit_add_rule() error path

If both 'tree' and 'watch' are valid we must call audit_put_tree(), just
like the preceding code within audit_add_rule().

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>