libbpf: fix return value for PERF_EVENT __arg_ctx type fix up check

If PERF_EVENT program has __arg_ctx argument with matching
architecture-specific pt_regs/user_pt_regs/user_regs_struct pointer
type, libbpf should still perform type rewrite for old kernels, but not
emit the warning. Fix copy/paste from kernel code where 0 is meant to
signify "no error" condition. For libbpf we need to return "true" to
proceed with type rewrite (which for PERF_EVENT program will be
a canonical `struct bpf_perf_event_data *` type).

Fixes: 9eea8fa ("libbpf: fix __arg_ctx type enforcement for perf_event programs")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240206002243.1439450-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/libbpf.c

@@ -6404,13 +6404,13 @@ static bool need_func_arg_type_fixup(const struct btf *btf, const struct bpf_pro
 	case BPF_PROG_TYPE_PERF_EVENT:
 		if (__builtin_types_compatible_p(bpf_user_pt_regs_t, struct pt_regs) &&
 		    btf_is_struct(t) && strcmp(tname, "pt_regs") == 0)
-			return 0;
+			return true;
 		if (__builtin_types_compatible_p(bpf_user_pt_regs_t, struct user_pt_regs) &&
 		    btf_is_struct(t) && strcmp(tname, "user_pt_regs") == 0)
-			return 0;
+			return true;
 		if (__builtin_types_compatible_p(bpf_user_pt_regs_t, struct user_regs_struct) &&
 		    btf_is_struct(t) && strcmp(tname, "user_regs_struct") == 0)
-			return 0;
+			return true;
 		break;
 	case BPF_PROG_TYPE_RAW_TRACEPOINT:
 	case BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE: