selftests/bpf: Fix prog_tests uprobe_autoattach compilation error

selftests/bpf: Fix prog_tests uprobe_autoattach compilation error

I am getting the following compilation error for prog_tests/uprobe_autoattach.c:

  tools/testing/selftests/bpf/prog_tests/uprobe_autoattach.c: In function ‘test_uprobe_autoattach’:
  ./test_progs.h:209:26: error: pointer ‘mem’ may be used after ‘free’ [-Werror=use-after-free]

The value of mem is now used in one of the asserts, which is why it may be
confusing compilers. However, it is not dereferenced. Silence this by moving
free(mem) after the assert block.

Fixes: 1717e248014c ("selftests/bpf: Uprobe tests should verify param/return values")
Signed-off-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220421132317.1583867-1-asavkov@redhat.com