Fix the use of 0 instead of NULL to clk_get() call. This stops the
following warning:
drivers/cpufreq/mvebu-cpufreq.c:73:40: warning: Using plain integer as NULL pointer
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>