apparmor: aa_label_alloc use aa_label_free on alloc failure

apparmor: aa_label_alloc use aa_label_free on alloc failure

aa_label_alloc() allocates a secid before allocating or taking the label
proxy. If the later proxy step fails, the error path only freed the label
memory, leaking any resources initialized by aa_label_init().

Use aa_label_free() on the failure path so partially initialized labels
release their secid and other label resources before the backing memory is
freed.

Fixes: f1bd904175e81 ("apparmor: add the base fns() for domain labels")
Signed-off-by: Zygmunt Krynicki <me@zygoon.pl>
Signed-off-by: John Johansen <john.johansen@canonical.com>