apparmor: fix a memleak in multi_transaction_new()

In the Linux kernel, the following vulnerability has been resolved:

apparmor: fix a memleak in multi_transaction_new()

In multi_transaction_new(), the variable t is not freed or passed out

on the failure of copy_from_user(t->data, buf, size), which could lead

to a memleak.

Fix this bug by adding a put_multi_transaction(t) in the error path.