hwmon: (coretemp) Fixup target cpu for package when cpu is offlined

When a CPU is offlined nothing checks whether it is the target CPU for the
package temperature sysfs interface.

As a consequence all future readouts of the package temperature return
crap:

90000

which is Tjmax of that package.

Check whether the outgoing CPU is the target for the package and assign it
to some other still online CPU in the package. Protect the change against
the rdmsr_on_cpu() in show_crit_alarm().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>