clk: simplify clk_core_get_parent_by_index()

Drop the "if (!core->parents)" case and refactor the function a bit
because core->parents is always allocated.  (Strictly speaking, it is
ZERO_SIZE_PTR if core->num_parents == 0, but such a case is omitted
by the if-conditional above.)
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/clk.c

@@ -350,12 +350,11 @@ static struct clk_core *clk_core_get_parent_by_index(struct clk_core *core,
 {
 	if (!core || index >= core->num_parents)
 		return NULL;
-	else if (!core->parents)
-		return clk_core_lookup(core->parent_names[index]);
-	else if (!core->parents[index])
-		return core->parents[index] =
+
+	if (!core->parents[index])
+		core->parents[index] =
 				clk_core_lookup(core->parent_names[index]);
-	else
+
 	return core->parents[index];
 }