ksmbd: fix wrong data area length for smb2 lock request

When turning debug mode on, The following error message from
ksmbd_smb2_check_message() is coming.

ksmbd: cli req padded more than expected. Length 112 not 88 for cmd:10 mid:14

data area length calculation for smb2 lock request in smb2_get_data_area_len() is
incorrect.

Fixes: e2f34481 ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>