tools: cpupower: Fix error when running cpupower monitor

get_cpu_topology() tries to get topology info from all cpus by reading
files in the topology sysfs dir. If a cpu is offlined, since it doesn't
have topology dir, this function fails and returns -1. This causes
functions relying on get_cpu_topology() to fail. For example-

$ cpupower monitor
Cannot read number of available processors

Fix this by skipping fetching topology info for offline cpus.
Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Reported-by: Pavaman Subramaniyam <pavsubra@linux.vnet.ibm.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

tools/power/cpupower/utils/helpers/topology.c

@@ -73,6 +73,8 @@ int get_cpu_topology(struct cpupower_topology *cpu_top)
 	for (cpu = 0; cpu < cpus; cpu++) {
 		cpu_top->core_info[cpu].cpu = cpu;
 		cpu_top->core_info[cpu].is_online = sysfs_is_cpu_online(cpu);
+		if (!cpu_top->core_info[cpu].is_online)
+			continue;
 		if(sysfs_topology_read_file(
 			cpu,
 			"physical_package_id",