[CPUFREQ] powernow-k7 build fix when ACPI=n

arch/x86/kernel/cpu/cpufreq/powernow-k7.c:172: warning: 'invalidate_entry' defined but not used
Reported-by: Toralf Förster <toralf.foerster@gmx.de>
Signed-off-by: Dave Jones <davej@redhat.com>

arch/x86/kernel/cpu/cpufreq/powernow-k7.c

@@ -168,10 +168,12 @@ static int check_powernow(void)
 	return 1;
 }
 
+#ifdef CONFIG_X86_POWERNOW_K7_ACPI
 static void invalidate_entry(unsigned int entry)
 {
 	powernow_table[entry].frequency = CPUFREQ_ENTRY_INVALID;
 }
+#endif
 
 static int get_ranges(unsigned char *pst)
 {