[POWERPC] cell: cbe_cpufreq cleanup and crash fix

cbe_cpufreq cleanups:

* comment format
* whitespace
* don't init on non-cell platforms

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Christian Krafft <krafft@de.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>