fix(st-clock): remove useless switch

This corrects MISRA C2012-16.6:
Every switch statement shall have at least two switch-clauses.
While at it, remove useless rate variable.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I123784e7184dbf4146fd0d7faeffd6a0382fc6a1
diff --git a/drivers/st/clk/clk-stm32-core.c b/drivers/st/clk/clk-stm32-core.c
index d166d54..9fe8c8c 100644
--- a/drivers/st/clk/clk-stm32-core.c
+++ b/drivers/st/clk/clk-stm32-core.c
@@ -466,10 +466,9 @@
 {
 	const struct clk_stm32 *clk = _clk_get(priv, id);
 	int parent;
-	unsigned long rate = 0UL;
 
 	if ((unsigned int)id >= priv->num) {
-		return rate;
+		return 0UL;
 	}
 
 	parent = _clk_stm32_get_parent(priv, id);
@@ -484,21 +483,14 @@
 			prate = _clk_stm32_get_rate(priv, parent);
 		}
 
-		rate = clk->ops->recalc_rate(priv, id, prate);
-
-		return rate;
+		return clk->ops->recalc_rate(priv, id, prate);
 	}
 
-	switch (parent) {
-	case CLK_IS_ROOT:
+	if (parent == CLK_IS_ROOT) {
 		panic();
-
-	default:
-		rate = _clk_stm32_get_rate(priv, parent);
-		break;
 	}
-	return rate;
 
+	return _clk_stm32_get_rate(priv, parent);
 }
 
 unsigned long _clk_stm32_get_parent_rate(struct stm32_clk_priv *priv, int id)