btrfs: remove redundant error check

While running btrfs_mksubvol(), d_really_is_positive() is called twice.
First in btrfs_mksubvol() and second inside btrfs_may_create(). So I
remove the first one.

Signed-off-by: Byongho Lee <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/ioctl.c

···
 	if (IS_ERR(dentry))
 		goto out_unlock;
 
-	error = -EEXIST;
-	if (d_really_is_positive(dentry))
-		goto out_dput;
-
 	error = btrfs_may_create(dir, dentry);
 	if (error)
 		goto out_dput;