ftdi: Avoid neutering lowlevel_device_info when opening it

ft232r.c

@@ -87,13 +87,9 @@ struct ft232r_device_handle {
 	uint16_t obufsz;
 };
 
-struct ft232r_device_handle *ft232r_open(struct lowlevel_device_info *info)
+struct ft232r_device_handle *ft232r_open(const struct lowlevel_device_info * const info)
 {
 	libusb_device * const dev = info->lowl_data;
-	info->lowl_data = NULL;
-	
-	if (!dev)
-		return NULL;
 	
 	// FIXME: Cleanup on errors
 	libusb_device_handle *devh;

ft232r.h

@@ -25,7 +25,7 @@ enum ft232r_reset_purge {
 
 struct ft232r_device_handle;
 
-extern struct ft232r_device_handle *ft232r_open(struct lowlevel_device_info *);
+extern struct ft232r_device_handle *ft232r_open(const struct lowlevel_device_info *);
 extern void ft232r_close(struct ft232r_device_handle *);
 extern bool ft232r_purge_buffers(struct ft232r_device_handle *, enum ft232r_reset_purge);
 extern bool ft232r_set_bitmode(struct ft232r_device_handle *, uint8_t mask, uint8_t mode);