MTD: Fix wrong check register_blkdev return value

register_blkdev return 1..255 when major = 0.

if (ret ) {
	printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
		tr->name, tr->major, ret);
	      mutex_unlock(&mtd_table_mutex);
	return ret;
}

Above code will return fail when register_blkdev return allocated major number.
Signed-off-by: NFrank Li <Frank.Li@freescale.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtd_blkdevs.c

@@ -502,13 +502,16 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	mutex_lock(&mtd_table_mutex);
 
 	ret = register_blkdev(tr->major, tr->name);
-	if (ret) {
+	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
 		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
+	if (ret)
+		tr->major = ret;
+
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);