drm/tilcdc: fix LCD pixel clock setting

The tilcdc_pclk_diff() compares the requested pixel clock rate to the
real one, so passing it clk_rate instead of clk_rate / clkdiv caused
it to fail even if the clk_rate was properly set. Adding the
real_pclk_rate variable makes the code more readable.
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20210322213337.26667-3-dariobin@libero.it

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

@@ -203,7 +203,7 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
-	unsigned long clk_rate, real_rate, pclk_rate;
+	unsigned long clk_rate, real_rate, real_pclk_rate, pclk_rate;
 	unsigned int clkdiv;
 	int ret;
 
@@ -214,7 +214,8 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
 
 	ret = clk_set_rate(priv->clk, pclk_rate * clkdiv);
 	clk_rate = clk_get_rate(priv->clk);
-	if (ret < 0 || tilcdc_pclk_diff(pclk_rate, clk_rate) > 5) {
+	real_pclk_rate = clk_rate / clkdiv;
+	if (ret < 0 || tilcdc_pclk_diff(pclk_rate, real_pclk_rate) > 5) {
 		/*
 		 * If we fail to set the clock rate (some architectures don't
 		 * use the common clock framework yet and may not implement