exynos: video: Rename variables for driver model

Use 'priv' for a private pointer and 'regs' for a register pointer.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>