drivers: spi: Fix SPI_DT_SPEC initializer for XCC toolchain

XCC (which is based on GCC 4.2) needs the initializer of one of the
union elements to be enclosed in brackets.

Signed-off-by: Maureen Helm <[email protected]>

Author: MaureenHelm

include/drivers/spi.h

@@ -251,7 +251,9 @@ struct spi_cs_control {
  */
 #define SPI_CS_CONTROL_PTR_DT(node_id, delay_)			  \
 	(&(struct spi_cs_control) {				  \
-		.gpio = SPI_CS_GPIOS_DT_SPEC_GET(node_id), \
+		{						  \
+			.gpio = SPI_CS_GPIOS_DT_SPEC_GET(node_id),\
+		},						  \
 		.delay = (delay_),				  \
 	})