selftests/bpf: fix a test for snprintf() overflow

The snprintf() function returns the number of bytes which *would*
have been copied if there were space. In other words, it can be
> sizeof(pin_path).

Fixes: c0fa1b6c3efc ("bpf: btf: Add BTF tests")
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Martin KaFai Lau <[e-mail]>
Link: https://lore.kernel.org/r/YtZ+aD/tZMkgOUw+@kili
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 	ret = snprintf(pin_path, sizeof(pin_path), "%s/%s",
 		       "/sys/fs/bpf", test->map_name);
 
-	if (CHECK(ret == sizeof(pin_path), "pin_path %s/%s is too long",
+	if (CHECK(ret >= sizeof(pin_path), "pin_path %s/%s is too long",
 		  "/sys/fs/bpf", test->map_name)) {
 		err = -1;
 		goto done;