drivers: i2s: Set DMA complete_callback flag

The MCUX LPC DMA driver now recognizes the compelete_callback
flag. Set this flag so we receive an interrupt after completion
of every block.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>

drivers/i2s/i2s_mcux_flexcomm.c

@@ -930,6 +930,7 @@ static int i2s_mcux_init(const struct device *dev)
 		.dma_cfg = {				\
 			.channel_direction = PERIPHERAL_TO_MEMORY,	\
 			.dma_callback = i2s_mcux_dma_rx_callback,	\
+			.complete_callback_en = true,			\
 			.block_count = NUM_RX_DMA_BLOCKS,		\
 		}							\
 	}