OMAPDSS: add dss_calc_clock_rates() back

dss_calc_clock_rates() was removed earlier as it was not used, but it is
needed for DSI PLL calculations, so this patch adds it back.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/dss.c b/drivers/video/omap2/dss/dss.c
index 456118b..d40653b 100644
--- a/drivers/video/omap2/dss/dss.c
+++ b/drivers/video/omap2/dss/dss.c
@@ -432,6 +432,29 @@
 	}
 }
 
+/* calculate clock rates using dividers in cinfo */
+int dss_calc_clock_rates(struct dss_clock_info *cinfo)
+{
+	if (dss.dpll4_m4_ck) {
+		unsigned long prate;
+
+		if (cinfo->fck_div > dss.feat->fck_div_max ||
+				cinfo->fck_div == 0)
+			return -EINVAL;
+
+		prate = clk_get_rate(clk_get_parent(dss.dpll4_m4_ck));
+
+		cinfo->fck = prate / cinfo->fck_div *
+			dss.feat->dss_fck_multiplier;
+	} else {
+		if (cinfo->fck_div != 0)
+			return -EINVAL;
+		cinfo->fck = clk_get_rate(dss.dss_clk);
+	}
+
+	return 0;
+}
+
 int dss_set_clock_div(struct dss_clock_info *cinfo)
 {
 	if (dss.dpll4_m4_ck) {