Fix broken kernel tracing in presence of offline CPUs

Offline CPUs may be encountered in a number of scenarios, for instance
in the presence of virtualization through VMware Workstation, where the
product advertises 128 CPUs as present, but then only makes a
(configurable) subset of these available and online for use.

utils/kernel.c

@@ -617,8 +617,13 @@ int record_kernel_trace_pipe(struct uftrace_kernel_writer *kernel, int cpu, int
 			goto retry;
 		if (errno == EAGAIN)
 			return 0;
-		else
-			return -errno;
+
+		// offline CPU
+		if (errno == ENODEV) {
+			return 0;
+		}
+
+		return -errno;
 	}
 
 	if (n == 0)