clk: sunxi: fix handling return value of of_property_match_string

The function can return negative values, so its result should
be assigned to signed variable.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/assign_signed_to_unsigned.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046107Signed-off-by: NAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

drivers/clk/sunxi/clk-sun8i-bus-gates.c

@@ -47,12 +47,12 @@ static void __init sun8i_h3_bus_gates_init(struct device_node *node)
 		return;
 
 	for (i = 0; i < ARRAY_SIZE(names); i++) {
-		index = of_property_match_string(node, "clock-names",
+		int idx = of_property_match_string(node, "clock-names",
 						   names[i]);
-		if (index < 0)
+		if (idx < 0)
 			return;
 
-		parents[i] = of_clk_get_parent_name(node, index);
+		parents[i] = of_clk_get_parent_name(node, idx);
 	}
 
 	clk_data = kmalloc(sizeof(struct clk_onecell_data), GFP_KERNEL);