ksmbd: don't open-code %pD

a bunch of places used %pd with file->f_path.dentry; shorter (and saner)
way to spell that is %pD with file...

Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steve French <stfrench@microsoft.com>