IB/hfi1: Add missing break in switch statement

Fix the following warning by adding a missing break:

drivers/infiniband/hw/hfi1/tid_rdma.c: In function ‘hfi1_tid_rdma_wqe_interlock’:
drivers/infiniband/hw/hfi1/tid_rdma.c:3251:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (prev->wr.opcode) {
   ^~~~~~
drivers/infiniband/hw/hfi1/tid_rdma.c:3259:2: note: here
  case IB_WR_RDMA_READ:
  ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.

Fixes: c6c23117 ("IB/hfi1: Add interlock between TID RDMA WRITE and other requests")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kaike Wan <Kaike.wan@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>