fix braino in "9p: fix ->rename_sem exclusion"

->d_op can bloody well be NULL

Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 30d61ef "9p: fix ->rename_sem exclusion"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/dcache.c

@@ -2967,11 +2967,11 @@ static int __d_unalias(struct dentry *dentry, struct dentry *alias)
 		goto out_err;
 	m2 = &alias->d_parent->d_inode->i_rwsem;
 out_unalias:
-	if (alias->d_op->d_unalias_trylock &&
+	if (alias->d_op && alias->d_op->d_unalias_trylock &&
 	    !alias->d_op->d_unalias_trylock(alias))
 		goto out_err;
 	__d_move(alias, dentry, false);
-	if (alias->d_op->d_unalias_unlock)
+	if (alias->d_op && alias->d_op->d_unalias_unlock)
 		alias->d_op->d_unalias_unlock(alias);
 	ret = 0;
 out_err: