boot: zephyr: Update USB CDC ACM device name

Follow the device name changes in Zephyr.

Signed-off-by: Filip Kubicz <filip.kubicz@nordicsemi.no>
diff --git a/boot/zephyr/serial_adapter.c b/boot/zephyr/serial_adapter.c
index 4fd6af7..c78480b 100644
--- a/boot/zephyr/serial_adapter.c
+++ b/boot/zephyr/serial_adapter.c
@@ -193,7 +193,7 @@
 #ifdef CONFIG_BOOT_SERIAL_UART
 	uart_dev = device_get_binding(DT_UART_CONSOLE_ON_DEV_NAME);
 #elif CONFIG_BOOT_SERIAL_CDC_ACM
-	uart_dev = device_get_binding(CONFIG_CDC_ACM_PORT_NAME_0);
+	uart_dev = device_get_binding(CONFIG_USB_CDC_ACM_DEVICE_NAME "_0");
 #endif
 	u8_t c;