uORB: Remove transfer of memory allocation ownership to CDev

- Allocate and free the node name in uORBDeviceNode.
- Add protected build support by de-allocating the name with kmm_free, when
  running in kernel side. strdup allocates from the kernel heap in NuttX kernel
  space.
- Remove the CDev::unregister_driver_and_memory(), it is no longer used

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

src/lib/cdev/CDev.cpp

@@ -128,6 +128,9 @@ CDev::init()
 		if (ret == PX4_OK) {
 			_registered = true;
 		}
+
+	} else {
+		ret = -ENODEV;
 	}
 
 	return ret;
@@ -373,27 +376,4 @@ CDev::remove_poll_waiter(px4_pollfd_struct_t *fds)
 	return -EINVAL;
 }
 
-int CDev::unregister_driver_and_memory()
-{
-	int retval = PX4_OK;
-
-	if (_registered) {
-		unregister_driver(_devname);
-		_registered = false;
-
-	} else {
-		retval = -ENODEV;
-	}
-
-	if (_devname != nullptr) {
-		free((void *)_devname);
-		_devname = nullptr;
-
-	} else {
-		retval = -ENODEV;
-	}
-
-	return retval;
-}
-
 } // namespace cdev

src/lib/cdev/CDev.hpp

@@ -270,17 +270,6 @@ protected:
 
 	px4_sem_t	_lock; /**< lock to protect access to all class members (also for derived classes) */
 
-
-	/**
-	* First, unregisters the driver. Next, free the memory for the devname,
-	* in case it was expected to have ownership. Sets devname to nullptr.
-	*
-	* This is only needed if the ownership of the devname was passed to the CDev, otherwise ~CDev handles it.
-	*
-	* @return  PX4_OK on success, -ENODEV if the devname is already nullptr
-	*/
-	int unregister_driver_and_memory();
-
 private:
 	const char	*_devname{nullptr};		/**< device node name */