add missing call to add new NAND devices

I forgot to add a call to the newly factored nand_device_add(), along
with its forward declaration.

src/flash/nand/tcl.c

@@ -580,6 +580,8 @@ static COMMAND_HELPER(create_nand_device, const char *bank_name,
 		return ERROR_OK;
 	}
 
+	nand_device_add(c);
+
 	return ERROR_OK;
 }