selftests/bpf: Initialize operation name before use

ASAN reports stack-buffer-overflow due to the uninitialized op_name.

Initialize it to fix the issue.

Fixes: 054b6c7 ("selftests/bpf: Add verifier log tests for BPF_BTF_LOAD command")
Signed-off-by: Leo Yan <leo.yan@arm.com>

Author: Leo-Yan

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

@@ -317,6 +317,7 @@ static void verif_btf_log_subtest(bool bad_btf)
 	res = load_btf(&opts, true);
 	ASSERT_EQ(res, -ENOSPC, "half_log_fd");
 	ASSERT_EQ(strlen(logs.buf), 24, "log_fixed_25");
+	strscpy(op_name, "log_fixed", sizeof(op_name));
 	ASSERT_STRNEQ(logs.buf, logs.reference, 24, op_name);
 
 	/* validate rolling verifier log logic: try all variations of log buf