cpufreq: imx6q: switch to Use clk_bulk_get() to refine clk operations

Use clk_bulk_get() to simplify the driver's clocks handling.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>