IB/hfi1: Remove set but not used variables 'offset' and 'fspsn'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/infiniband/hw/hfi1/tid_rdma.c: In function tid_rdma_rcv_error:
drivers/infiniband/hw/hfi1/tid_rdma.c:2029:7: warning: variable offset set but not used [-Wunused-but-set-variable]
drivers/infiniband/hw/hfi1/tid_rdma.c: In function hfi1_rc_rcv_tid_rdma_ack:
drivers/infiniband/hw/hfi1/tid_rdma.c:4555:35: warning: variable fspsn set but not used [-Wunused-but-set-variable]

'offset' is never used since introduction in
commit d0d564a1 ("IB/hfi1: Add functions to receive TID RDMA READ request")

'fspsn' is never used since introduciotn in
commit 9e93e967 ("IB/hfi1: Add a function to receive TID RDMA ACK packet")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>