RDMA/iser: struct iscsi_iser_task is declared twice

struct iscsi_iser_task has been declared at 201st line. Remove the
duplicate.

Link: https://lore.kernel.org/r/20210326113347.903976-1-wanjiabing@vivo.com


Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>