cpuidle: big_little: Simplify with of_machine_device_match()

Replace open-coded getting root OF node and matching against it with
new of_machine_device_match() helper.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

drivers/cpuidle/cpuidle-big_little.c

···
 static int __init bl_idle_init(void)
 {
 	int ret;
-	struct device_node *root = of_find_node_by_path("/");
-	const struct of_device_id *match_id;
-
-	if (!root)
-		return -ENODEV;
 
 	/*
 	 * Initialize the driver just for a compliant set of machines
 	 */
-	match_id = of_match_node(compatible_machine_match, root);
-
-	of_node_put(root);
-
-	if (!match_id)
+	if (!of_machine_device_match(compatible_machine_match))
 		return -ENODEV;
 
 	if (!mcpm_is_available())