ksmbd: Fix the missing xa_store error check

xa_store() can fail, it return xa_err(-EINVAL) if the entry cannot
be stored in an XArray, or xa_err(-ENOMEM) if memory allocation failed,
so check error for xa_store() to fix it.

Cc: stable@vger.kernel.org
Fixes: b685757c ("ksmbd: Implements sess->rpc_handle_list as xarray")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>