dm: ls1021aqds: dts: Use "spi_dataflash" driver instead of "spi_flash_std" for DSPI flash

The type of DSPI flash on ls1021aqds is AT45DB021, it has specail
commands and page-size.
Use the special spi flash driver instead of "spi_flash_std" driver.

Signed-off-by: Haikun Wang <haikun.wang@freescale.com>
Tested-by: Haikun Wang <haikun.wang@freescale.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jteki@openedev.com>

arch/arm/dts/ls1021a-qds.dts

@@ -30,7 +30,7 @@
 	dspiflash: at45db021d@0 {
 		#address-cells = <1>;
 		#size-cells = <1>;
-		compatible = "spi-flash";
+		compatible = "atmel,dataflash";
 		spi-max-frequency = <16000000>;
 		spi-cpol;
 		spi-cpha;