[CPUFREQ] EXYNOS4210: update the name of EXYNOS clock register

According to replacing the name of EXYNOS clock registers,
this patch updates exynos4210-cpufreq.c file where it is used.

Cc: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Dave Jones <davej@redhat.com>