nrf: neopixel chains of certain lengths cause hard fault

[dhalbert]

Found by @bmeisels in #circuitpython discord. Reduced to simple test case:

>>> import neopixel,board
>>> px = neopixel.NeoPixel(board.D6, 1)
>>> px[0] = (5,5,5)
>>> px.deinit()
>>> px = neopixel.NeoPixel(board.D6, 2)
>>> px[0] = (5,5,5)
[hard crash]

In general, it fails for neopixel.NeoPixel(board.D6, <n>) for n = 2 through 5, then it works for 6 and above.

[tannewt]

Fixed by #1963