rgbmatrix: Avoid leaving an incompletely configured display bus #15786

Job	Run time
scheduler	47s
docs	11m 50s
mpy-cross-mac	1m 11s
windows	0s
tests / run (all)	45s
tests / run (mpy)	36s
tests / run (native)	42s
mpy-cross / build (static)	21s
tests / run (native_mpy)	36s
mpy-cross / build (static-aarch64)	33s
mpy-cross / build (static-mingw)	49s
mpy-cross / build (static-raspbian)	44s
ports (atmel-samd) / board (itsybitsy_m4_express)	8m 33s
	27m 27s

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