iio: adc: nxp-sar-adc: zero-initialize dma_slave_config

iio: adc: nxp-sar-adc: zero-initialize dma_slave_config

nxp_sar_adc_start_cyclic_dma() only fills the RX-side members of
dma_slave_config before passing it to dmaengine_slave_config().

Zero-initialize the structure so unused members do not contain stack
garbage. Some DMA engines consult optional dma_slave_config fields, so
leaving them uninitialized can cause DMA setup failures.

Fixes: 4434072a893e ("iio: adc: Add the NXP SAR ADC support for the s32g2/3 platforms")
Signed-off-by: Shuvam Pandey <shuvampandey1@gmail.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>