ext4: remove redundant operation that set bh to NULL

The out_fail branch path don't release the bh and the second bh is
valid only in the for statement, so we don't need to set them to NULL.
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Link: https://lore.kernel.org/r/1603194069-17557-1-git-send-email-kaixuxia@tencent.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -4074,7 +4074,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (IS_ERR(bh)) {
 		ext4_msg(sb, KERN_ERR, "unable to read superblock");
 		ret = PTR_ERR(bh);
-		bh = NULL;
 		goto out_fail;
 	}
 	/*
@@ -4703,7 +4702,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			       "can't read group descriptor %d", i);
 			db_count = i;
 			ret = PTR_ERR(bh);
-			bh = NULL;
 			goto failed_mount2;
 		}
 		rcu_read_lock();