x86: fix section mismatch warning in mcheck/mce_64.c

Fix following warning:
WARNING: arch/x86/kernel/cpu/mcheck/built-in.o(.text+0x752): Section mismatch: reference to .cpuinit.text:mce_create_device in 'mce_cpu_callback'

mce_cpu_callback() is only used by mce_cpu_notofier.
The notifier is only used for hotplugable cpu's as it is
registered using register_hotcpu_notifier(),

Annotate them both __cpuinit to fix the warning.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>