ksmbd: fix uninitialized pointer read in ksmbd_vfs_rename()

Uninitialized rd.delegated_inode can be used in vfs_rename().
Fix this by setting rd.delegated_inode to NULL to avoid the uninitialized
read.

Fixes: 74d7970f

 ("ksmbd: fix racy issue from using ->d_parent and ->d_name")
Reported-by: Coverity Scan <scan-admin@coverity.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>