MIPS: loongson2_cpufreq: Fix CPU clock rate setting mismerge

MIPS: loongson2_cpufreq: Fix CPU clock rate setting mismerge

During 3.16 merge window, parts of the commit 8e8acb32960f
(MIPS/loongson2_cpufreq: Fix CPU clock rate setting) seem to have
been deleted probably due to a mismerge, and as a result cpufreq
is broken again on Loongson2 boards in 3.16 and newer kernels.
Fix by repeating the fix.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: stable@vger.kernel.org # 3.16
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7835/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>