spi: spi-pic32: Fix issue with uninitialized dma_slave_config

Depending on the DMA driver being used, the struct dma_slave_config may
need to be initialized to zero for the unused data.

For example, we have three DMA drivers using src_port_window_size and
dst_port_window_size. If these are left uninitialized, it can cause DMA
failures.

For spi-pic32, this is probably not currently an issue but is still good to
fix though.

Fixes: 1bcb9f8ceb67 ("spi: spi-pic32: Add PIC32 SPI master driver")
Cc: Purna Chandra Mandal <[e-mail]>
Cc: Peter Ujfalusi <[e-mail]>
Cc: Vinod Koul <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-pic32.c

···
 	struct dma_slave_config cfg;
 	int ret;
 
+	memset(&cfg, 0, sizeof(cfg));
 	cfg.device_fc = true;
 	cfg.src_addr = pic32s->dma_base + buf_offset;
 	cfg.dst_addr = pic32s->dma_base + buf_offset;