spi: fix explicit controller deregistration

spi: fix explicit controller deregistration

Johan Hovold <johan@kernel.org> says:

Turns out we have a few drivers that get the tear down ordering wrong
also when not using device managed registration (cf. [1] and [2]).

Fix this to avoid issues like system errors due to unclocked accesses,
NULL-pointer dereferences, hangs or failed I/O during during
deregistration (e.g. when powering down devices).

Johan

[1] https://lore.kernel.org/lkml/20260409120419.388546-2-johan@kernel.org/
[2] https://lore.kernel.org/lkml/20260410081757.503099-1-johan@kernel.org/