hwmon: (coretemp) Check for null before removing sysfs attrs

If coretemp_add_core() gets an error then pdata->core_data[indx]
is already NULL and has been kfreed. Don't pass that to
sysfs_remove_group() as that will crash in sysfs_remove_group().

[Shortened for readability]
[91854.020159] sysfs: cannot create duplicate filename '/devices/platform/coretemp.0/hwmon/hwmon2/temp20_label'
<cpu offline>
[91855.126115] BUG: kernel NULL pointer dereference, address: 0000000000000188
[91855.165103] #PF: supervisor read access in kernel mode
[91855.194506] #PF: error_code(0x0000) - not-present page
[91855.224445] PGD 0 P4D 0
[91855.238508] Oops: 0000 [#1] PREEMPT SMP PTI
...
[91855.342716] RIP: 0010:sysfs_remove_group+0xc/0x80
...
[91855.796571] Call Trace:
[91855.810524]  coretemp_cpu_offline+0x12b/0x1dd [coretemp]
[91855.841738]  ? coretemp_cpu_online+0x180/0x180 [coretemp]
[91855.871107]  cpuhp_invoke_callback+0x105/0x4b0
[91855.893432]  cpuhp_thread_fun+0x8e/0x150
...

Fix this by checking for NULL first.
Signed-off-by: Phil Auld <pauld@redhat.com>
Cc: linux-hwmon@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221117162313.3164803-1-pauld@redhat.com
Fixes: 199e0de7 ("hwmon: (coretemp) Merge pkgtemp with coretemp")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/coretemp.c

@@ -533,6 +533,10 @@ static void coretemp_remove_core(struct platform_data *pdata, int indx)
 {
 	struct temp_data *tdata = pdata->core_data[indx];
 
+	/* if we errored on add then this is already gone */
+	if (!tdata)
+		return;
+
 	/* Remove the sysfs attributes */
 	sysfs_remove_group(&pdata->hwmon_dev->kobj, &tdata->attr_group);