apparmor: fix memory leak in verify_header

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

apparmor: fix memory leak in verify_header

The function sets `*ns = NULL` on every call, leaking the namespace

string allocated in previous iterations when multiple profiles are

unpacked. This also breaks namespace consistency checking since *ns

is always NULL when the comparison is made.

Remove the incorrect assignment.

The caller (aa_unpack) initializes *ns to NULL once before the loop,

which is sufficient.