drm/exynos: rotator: convert to common clock framework

This driver was not used after introduction of common clock framework.
This patch adds missing prepare/unprepare calls and allows to use it
again with current kernel code.

Signed-off-by: Marek Szyprowski <[e-mail]>
Reviewed-by: Gustavo Padovan <[e-mail]>
Signed-off-by: Inki Dae <[e-mail]>

drivers/gpu/drm/exynos/exynos_drm_rotator.c

···
 static int rotator_clk_crtl(struct rot_context *rot, bool enable)
 {
 	if (enable) {
-		clk_enable(rot->clock);
+		clk_prepare_enable(rot->clock);
 		rot->suspended = false;
 	} else {
-		clk_disable(rot->clock);
+		clk_disable_unprepare(rot->clock);
 		rot->suspended = true;
 	}