spi: s3c64xx: Disable IRQ mode when using DMA

Fixing the problem of enabling DMA mode and IRQ mode at the same time.
In this case, a value of more than 6bits is written to RDY_LVL, it can
cause an invasion of other registers, potentially leading to SPI
transfer failure.

Fixes: 1ee80671 ("spi: s3c64xx: support interrupt based pio mode")
Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230510113942.89994-1-jaewon02.kim@samsung.com


Signed-off-by: Mark Brown <broonie@kernel.org>