x86, k8: Fix section mismatch for powernowk8_exit()

Fix the following warning:

"WARNING: arch/x86/kernel/built-in.o(.exit.text+0x72):
Section mismatch in reference from the function powernowk8_exit() to the variable .cpuinit.data:cpb_nb

The function __exit powernowk8_exit() references a variable
__cpuinitdata cpb_nb. This is often seen when error handling in the exit
function uses functionality in the init path. The fix is often to remove
the __cpuinitdata annotation of cpb_nb so it may be used outside an init
section."

Cc: <stable@kernel.org>
Reported-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20100525152858.GA24836@aftab>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>