cpufreq: loongson2: fix regression related to clock management

Commit 42913c79 (MIPS: Loongson2: Use clk API instead of direct
dereferences) broke the cpufreq functionality on Loongson2 boards:
clk_set_rate() is called before the CPU frequency table is
initialized, and therefore will always fail.

Fix by moving the clk_set_rate() after the table initialization.
Tested on Lemote FuLoong mini-PC.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: 3.9+ <stable@vger.kernel.org> # 3.9+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>