cpufreq: airoha: modify CONFIG_OF dependency

Compile-testing without CONFIG_OF leads to a harmless build warning:

drivers/cpufreq/airoha-cpufreq.c:109:34: error: 'airoha_cpufreq_match_list' defined but not used [-Werror=unused-const-variable=]
  109 | static const struct of_device_id airoha_cpufreq_match_list[] __initconst = {
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~

It would be possible to mark the variable as __maybe_unused to shut up
that warning, but a Kconfig dependency seems more appropriate as this still
allows build testing in allmodconfig and randconfig builds on all
architectures.

An earlier commit, b865a840 ("cpufreq: airoha: Depends on OF"),
tried to fix it incorrectly. ARCH_AIROHA already requires CONFIG_OF, so
this change does nothing, and the dependency is still missing for the
COMPILE_TEST case.

Fix it properly.

Fixes: 84cf9e54 ("cpufreq: airoha: Add EN7581 CPUFreq SMCCC driver")
Fixes: b865a840 ("cpufreq: airoha: Depends on OF")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[ Viresh: updated commit log and fixed rebase conflict ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/9d51d2710061dfa7f2568287c6ed125b858b7318.1738580005.git.viresh.kumar@linaro.org


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>