spi: s3c64xx: fix NULL-deref on driver unbind

spi: s3c64xx: fix NULL-deref on driver unbind

A change moving DMA channel allocation from probe() back to
s3c64xx_spi_prepare_transfer() failed to remove the corresponding
deallocation from remove().

Drop the bogus DMA channel release from remove() to avoid triggering a
NULL-pointer dereference on driver unbind.

This issue was flagged by Sashiko when reviewing a controller
deregistration fix.

Fixes: f52b03c70744 ("spi: s3c64xx: requests spi-dma channel only during data transfer")
Cc: stable@vger.kernel.org	# 6.0
Cc: Adithya K V <adithya.kv@samsung.com>
Link: https://sashiko.dev/#/patchset/20260410081757.503099-1-johan%40kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260410094925.518343-1-johan@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>