S3C64XX: Fix ARMCLK configuration

The value of armclk_mask needs to be inverted for use as a mask on
the register value when updating ARM_RATIO.

This is critical for cpufreq support, without it attempts to scale
the frequency of the core trash pretty much the entire clock tree.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>