exynos: clock: use the clear and set bits macros.

Use setbits/clrbits macro instead of readl/writel function.
(Suggested by Wolfgang)

Signed-off-by: Inha Song <ideal.song@samsung.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>