platform/x86/intel-uncore-freq: Fix current_freq_khz after CPU hotplug

platform/x86/intel-uncore-freq: Fix current_freq_khz after CPU hotplug

When the last CPU of a legacy uncore die goes offline,
uncore_freq_remove_die_entry() clears control_cpu. During CPU hotplug
re-add, uncore_freq_add_entry() still populates sysfs attributes before
assigning the new control CPU. As a result, the current frequency read
returns -ENXIO and current_freq_khz is omitted from the recreated sysfs
group.

Assign control_cpu before the initial read paths and before
create_attr_group() so sysfs recreation uses the new online CPU. If
sysfs creation fails, restore control_cpu to -1 to keep the error path
state consistent.

Fixes: 4d73c6772ab7 ("platform/x86: intel-uncore-freq: Conditionally create attribute for read frequency")
Cc: stable@vger.kernel.org
Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260602020752.3126-1-weiguixiong@bytedance.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>