bpf: Fix an error code in check_btf_func()

This code returns success if the "info_aux" allocation fails but it
should return -ENOMEM.

Fixes: 8c1b6e69 ("bpf: Compare BTF types of functions arguments with actual types")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200604085436.GA943001@mwanda