device: make device_register() clone the device

This is expected by the callers, but this fact was hidden well within
the old list implementation.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

include/devices.h

@@ -94,6 +94,7 @@ int	devices_init (void);
 int	device_deregister(char *devname);
 struct list_head* device_get_list(void);
 device_t* device_get_by_name(char* name);
+device_t* device_clone(device_t *dev);
 
 #ifdef CONFIG_LCD
 int	drv_lcd_init (void);