cpufreq: s3c64xx: Fix compilation warning

cpufreq: s3c64xx: Fix compilation warning

The driver generates following warning when regulator support isn't
enabled in the kernel. Fix it.

   drivers/cpufreq/s3c64xx-cpufreq.c: In function 's3c64xx_cpufreq_set_target':
>> drivers/cpufreq/s3c64xx-cpufreq.c:55:22: warning: variable 'old_freq' set but not used [-Wunused-but-set-variable]
      55 |         unsigned int old_freq, new_freq;
         |                      ^~~~~~~~
>> drivers/cpufreq/s3c64xx-cpufreq.c:54:30: warning: variable 'dvfs' set but not used [-Wunused-but-set-variable]
      54 |         struct s3c64xx_dvfs *dvfs;
         |                              ^~~~

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501191803.CtfT7b2o-lkp@intel.com/
Cc: 5.4+ <stable@vger.kernel.org> # v5.4+
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/236b227e929e5adc04d1e9e7af6845a46c8e9432.1737525916.git.viresh.kumar@linaro.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>