dcache: fix outdated DCACHE_NEED_LOOKUP comment

The DCACHE_NEED_LOOKUP case referred to here was removed with
39e3c9553f34381a1b664c27b0c696a266a5735e "vfs: remove
DCACHE_NEED_LOOKUP".

There are only four real_lookup() callers and all of them pass in an
unhashed dentry just returned from d_alloc.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1298,8 +1298,8 @@ static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir,
 }
 
 /*
- * Call i_op->lookup on the dentry.  The dentry must be negative but may be
- * hashed if it was pouplated with DCACHE_NEED_LOOKUP.
+ * Call i_op->lookup on the dentry.  The dentry must be negative and
+ * unhashed.
  *
  * dir->d_inode->i_mutex must be held
  */