spi: lpspi: disable lpspi module irq in DMA mode

When all bits of IER are set to 0, we still can observe the lpspi irq events
when using DMA mode to transfer data.

So disable irq to avoid the too much irq events.

Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Link: https://lore.kernel.org/r/20230505063557.3962220-1-xiaoning.wang@nxp.com


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