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

In the Linux kernel, the following vulnerability has been resolved:

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.