hwmon: (coretemp) Use proper error codes in cpu online callback

The cpu online callback returns success unconditionally even when the
device has no support, micro code mismatches or device allocation fails.
Only if CPU_HOTPLUG is disabled, the init function checks whether the
device list is empty and removes the driver.

This does not make sense. If CPU HOTPLUG is enabled then there is no point
to keep the driver around when it failed to initialize on the already
online cpus. The chance that not yet online CPUs will provide a functional
interface later is very close to zero.

Add proper error return codes, so the setup of the cpu hotplug states fails
when the device cannot be initialized and remove all the magic cruft.

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