cifs: more breakage on mount failures

if cifs_get_root() fails, we end up with ->mount() returning NULL,
which is not what callers expect.  Moreover, in case of superblock
reuse we end up leaking a superblock reference...
Acked-by: NPavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/cifs/cifsfs.c

@@ -710,19 +710,16 @@ cifs_do_mount(struct file_system_type *fs_type,
 
 	sb->s_flags |= MS_ACTIVE;
 
+out_shared:
 	root = cifs_get_root(volume_info, sb);
-	if (root == NULL)
+	if (root == NULL) {
+		root = ERR_PTR(-EINVAL); /* XXX */
 		goto out_super;
+	}
 
 	cFYI(1, "dentry root is: %p", root);
 	goto out;
 
-out_shared:
-	root = cifs_get_root(volume_info, sb);
-	if (root)
-		cFYI(1, "dentry root is: %p", root);
-	goto out;
-
 out_super:
 	deactivate_locked_super(sb);
 out: