Staging: zram: Fix memory leak by refcount mismatch

As suggested by Minchan Kim and Jerome Marchand "The code in reset_store
get the block device (bdget_disk()) but it does not put it (bdput()) when
it's done using it. The usage count is therefore incremented but never
decremented."

This patch also puts bdput() for all error cases.
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zram/zram_drv.c

@@ -652,21 +652,30 @@ static ssize_t reset_store(struct device *dev,
 		return -ENOMEM;
 
 	/* Do not reset an active device! */
-	if (bdev->bd_holders)
-		return -EBUSY;
+	if (bdev->bd_holders) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	ret = kstrtou16(buf, 10, &do_reset);
 	if (ret)
-		return ret;
+		goto out;
 
-	if (!do_reset)
-		return -EINVAL;
+	if (!do_reset) {
+		ret = -EINVAL;
+		goto out;
+	}
 
 	/* Make sure all pending I/O is finished */
 	fsync_bdev(bdev);
+	bdput(bdev);
 
 	zram_reset_device(zram, true);
 	return len;
+
+out:
+	bdput(bdev);
+	return ret;
 }
 
 static void __zram_make_request(struct zram *zram, struct bio *bio, int rw)