mmc_block: handle error from mmc_register_driver()

Check error from mmc_register_driver() and properly unwind
block device registration.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/card/block.c

@@ -613,14 +613,19 @@ static struct mmc_driver mmc_driver = {
 
 static int __init mmc_blk_init(void)
 {
-	int res = -ENOMEM;
+	int res;
 
 	res = register_blkdev(MMC_BLOCK_MAJOR, "mmc");
 	if (res)
 		goto out;
 
-	return mmc_register_driver(&mmc_driver);
+	res = mmc_register_driver(&mmc_driver);
+	if (res)
+		goto out2;
 
+	return 0;
+ out2:
+	unregister_blkdev(MMC_BLOCK_MAJOR, "mmc");
  out:
 	return res;
 }