drivers: spi: xmc4xxx: Fix potential runtime error

Fixes an unhandled interrupt runtime crash if CONFIG_SPI_XMC4XXX_DMA=y and
CONFIG_SPI_XMC4XXX_INTERRUPT=n.

The unhandled interrupt error is triggered because irq_enable() was called
without calling IRQ_CONNECT() when CONFIG_SPI_XMC4XXX_INTERRUPT=n.

Signed-off-by: Andriy Gelman <andriy.gelman@gmail.com>

drivers/spi/spi_xmc4xxx.c

@@ -468,7 +468,9 @@ static int spi_xmc4xxx_transceive_dma(const struct device *dev, const struct spi
 		spi_context_cs_control(ctx, false);
 	}
 
+#if defined(CONFIG_SPI_XMC4XXX_INTERRUPT)
 	irq_enable(config->irq_num_rx);
+#endif
 	spi_context_release(ctx, ret);
 
 	return ret;

tests/drivers/spi/spi_loopback/boards/xmc45_relax_kit.conf

@@ -1,3 +1,2 @@
-CONFIG_SPI_XMC4XXX_INTERRUPT=y
 CONFIG_SPI_XMC4XXX_DMA=y
 CONFIG_SPI_LOOPBACK_MODE_LOOP=y