dmaengine: lpc32xx-dmamux: fix device leak on route allocation

dmaengine: lpc32xx-dmamux: fix device leak on route allocation

Make sure to drop the reference taken when looking up the DMA mux
platform device during route allocation.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

Fixes: 5d318b595982 ("dmaengine: Add dma router for pl08x in LPC32XX SoC")
Cc: stable@vger.kernel.org	# 6.12
Cc: Piotr Wojtaszczyk <piotr.wojtaszczyk@timesys.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Link: https://patch.msgid.link/20251117161258.10679-9-johan@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>