smb: server: remove useless casts from KSMBD_TRANS/SMBD_TRANS

smb: server: remove useless casts from KSMBD_TRANS/SMBD_TRANS

At best they gain nothing, at worst we procude real bugs.
Note container_of() already casts to a pointer of the
given type.

Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>