selftests/bpf: Fix bpf_link leak in ns_current_pid_tgid selftest

If condition is inverted, but it's also just not necessary.

Fixes: 1c1052e0 ("tools/testing/selftests/bpf: Add self-tests for new helper bpf_get_ns_current_pid_tgid.")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: Carlos Neira <cneirabustos@gmail.com>
Link: https://lore.kernel.org/bpf/20200429012111.277390-11-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c

@@ -80,9 +80,6 @@ void test_ns_current_pid_tgid(void)
 		  "User pid/tgid %llu BPF pid/tgid %llu\n", id, bss.pid_tgid))
 		goto cleanup;
 cleanup:
-	if (!link) {
 	bpf_link__destroy(link);
-		link = NULL;
-	}
 	bpf_object__close(obj);
 }