d_hash_and_lookup(): export, switch open-coded instances

* calling conventions change - ERR_PTR() is returned on ->d_hash() errors;
NULL is just for dcache miss now.
* exported, open-coded instances in ncpfs and cifs converted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index 7255b0c..df40cc5 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -82,12 +82,10 @@
 
 	cFYI(1, "%s: for %s", __func__, name->name);
 
-	if (parent->d_op && parent->d_op->d_hash)
-		parent->d_op->d_hash(parent, parent->d_inode, name);
-	else
-		name->hash = full_name_hash(name->name, name->len);
+	dentry = d_hash_and_lookup(parent, name);
+	if (unlikely(IS_ERR(dentry)))
+		return;
 
-	dentry = d_lookup(parent, name);
 	if (dentry) {
 		int err;