cpufreq: exynos5440: Fix potential NULL pointer dereference

If 'dvfs_info' is NULL (due to devm_kzalloc failure) the failure
error message would try to dereference it. Use 'pdev' instead.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>