cpufreq: armada-37xx: Remove set but not used variable 'freq'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/cpufreq/armada-37xx-cpufreq.c: In function 'armada37xx_cpufreq_avs_setup':
drivers/cpufreq/armada-37xx-cpufreq.c:260:28: warning:
 variable 'freq' set but not used [-Wunused-but-set-variable]

It's never used since introduction in commit 1c352823

 ("cpufreq:
armada-37xx: Add AVS support")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>