ksmbd: add missing assignments to ret on ndr_read_int64 read calls

Currently there are two ndr_read_int64 calls where ret is being checked
for failure but ret is not being assigned a return value from the call.
Static analyis is reporting the checks on ret as dead code.  Fix this.

Addresses-Coverity: ("Logical dead code")
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>