cpufreq: loongson2_cpufreq: adjust cpufreq uses of LOONGSON_CHIPCFG

The post-fork cleanup of loongson2ef from loongson64 changed
LOONGSON_CHIPCFG from a single-argument functional macro to a
non-functional macro with an mmio address in loongson2ef, but
loongson2_cpufreq still uses the notation of a functional macro call
expecting it to be an lvalue.  Fixed based on loongson_suspend_enter.

Signed-off-by: Alexandre Oliva <lxoliva@fsfla.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>