cpufreq: loongson1: Add missing MODULE_ALIAS

This patch adds missing MODULE_ALIAS for automatic loading of this cpufreq
driver when it is compiled as an external module.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: a0a22cf1 ("cpufreq: Loongson1: Add cpufreq driver for Loongson1B")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>