hwmon: (coretemp) fix section mismatch warning

Fix following warning:
WARNING: vmlinux.o(.text+0xebfd04): Section mismatch in reference from the function coretemp_cpu_callback() to the function .cpuinit.text:coretemp_device_add()

coretemp_cpu_callback() are only used inside a
HOTPLUG_CPU block so annotate it __cpuinit.
The notifier referencing the function are annotated
__refdata to silence warning from the exit function.
The unregister function do not use the embedded pointer
but clears the variable so the annotation is OK.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>