clk: mvebu: armada-37xx-periph: remove .set_parent method for CPU PM clock

Remove the .set_parent method in clk_pm_cpu_ops.

This method was supposed to be needed by the armada-37xx-cpufreq driver,
but was never actually called due to wrong assumptions in the cpufreq
driver. After this was fixed in the cpufreq driver, this method is not
needed anymore.

Signed-off-by: Marek Behún <kabel@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Tested-by: Pali Rohár <pali@kernel.org>
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: 2089dc33 ("clk: mvebu: armada-37xx-periph: add DVFS support for cpu clocks")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>