spi: spi-xilinx: Remove redundant platform_set_drvdata()

Setting platform data to NULL is not necessary.
Also fixes the following sparse warning:
drivers/spi/spi-xilinx.c:508:35: warning: Using plain integer as NULL pointer
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-xilinx.c

@@ -534,7 +534,6 @@ static int xilinx_spi_probe(struct platform_device *dev)
 static int xilinx_spi_remove(struct platform_device *dev)
 {
 	xilinx_spi_deinit(platform_get_drvdata(dev));
-	platform_set_drvdata(dev, 0);
 
 	return 0;
 }