RDMA/qedr: Fix endian problems around imm_data

The double swap matches what user space rdma-core does to imm_data.

wc->imm_data is not used in the kernel so this change has no practical
impact.

Acked-by: Michal Kalderon <michal.kalderon@cavium.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>