drm/stm: ltdc: restore calls to clk_{enable/disable}

Restore calls to clk_{enable/disable} deleted after applying the wrong
version of the patch

Fixes: fd6905fc ("drm/stm: ltdc: remove clk_round_rate comment")
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Acked-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190527115830.15836-1-benjamin.gaignard@st.com

drivers/gpu/drm/stm/ltdc.c

@@ -507,10 +507,12 @@ static bool ltdc_crtc_mode_fixup(struct drm_crtc *crtc,
 	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
 	int rate = mode->clock * 1000;
 
+	clk_disable(ldev->pixel_clk);
 	if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
 		DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
 		return false;
 	}
+	clk_enable(ldev->pixel_clk);
 
 	adjusted_mode->clock = clk_get_rate(ldev->pixel_clk) / 1000;