cpufreq: sun50i: Add missing MODULE_DEVICE_TABLE

This patch adds missing MODULE_DEVICE_TABLE definition which generates
correct modalias for automatic loading of this cpufreq driver when it is
compiled as an external module.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: f328584f ("cpufreq: Add sun50i nvmem based CPU scaling driver")
Reviewed-by: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>