MAINTAINERS: mark rsi wifi driver as orphan

Neither Redpine Signals nor Silicon Labs seem to care about proper
maintenance of this driver, nor is there any help, documentation or
feedback on patches. The driver suffers from various problems and
subtle bugs. Mark it as orphaned.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221113185838.11643-1-marex@denx.de