make d_splice_alias(ERR_PTR(err), dentry) = ERR_PTR(err)

... and simplify the living hell out of callers

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index b754b77..707d605 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1037,15 +1037,11 @@
 			return ERR_PTR(-EIO);
 		}
 		inode = ext4_iget(dir->i_sb, ino);
-		if (IS_ERR(inode)) {
-			if (PTR_ERR(inode) == -ESTALE) {
-				EXT4_ERROR_INODE(dir,
-						 "deleted inode referenced: %u",
-						 ino);
-				return ERR_PTR(-EIO);
-			} else {
-				return ERR_CAST(inode);
-			}
+		if (inode == ERR_PTR(-ESTALE)) {
+			EXT4_ERROR_INODE(dir,
+					 "deleted inode referenced: %u",
+					 ino);
+			return ERR_PTR(-EIO);
 		}
 	}
 	return d_splice_alias(inode, dentry);