spi/spi_s3c24xx: Use spi_bitbang_stop instead of spi_unregister_master in s3c24xx_spi_remove

Calling spi_bitbang_stop() will also destroy bitbang->workqueue,
which is created by calling spi_bitbang_start() in s3c24xx_spi_probe().
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi_s3c24xx.c

@@ -668,7 +668,7 @@ static int __exit s3c24xx_spi_remove(struct platform_device *dev)
 
 	platform_set_drvdata(dev, NULL);
 
-	spi_unregister_master(hw->master);
+	spi_bitbang_stop(&hw->bitbang);
 
 	clk_disable(hw->clk);
 	clk_put(hw->clk);