Correct collect of permanent pointers.
Correct collect of permanent pointers.

The previous implementation managed to keep all but the head
pointer of the list.

Fixes #1814

adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython