cpufreq: armada-37xx: Fix determining base CPU frequency

When current CPU load is not L0 then loading armada-37xx-cpufreq.ko driver
fails with following error:

    # modprobe armada-37xx-cpufreq
    [  502.702097] Unsupported CPU frequency 250 MHz

This issue was partially fixed by commit 8db82563 ("cpufreq:
armada-37xx: fix frequency calculation for opp"), but only for calculating
CPU frequency for opp.

Fix this also for determination of base CPU frequency.

Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Tomasz Maciej Nowak <tmn505@gmail.com>
Tested-by: Anders Trier Olesen <anders.trier.olesen@gmail.com>
Tested-by: Philip Soares <philips@netisense.com>
Fixes: 92ce45fb ("cpufreq: Add DVFS support for Armada 37xx")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>