rdma/cxgb4: Fix SRQ endianness annotations

This patch avoids that sparse complains about casts to restricted __be32.

Fixes: a3cdaa69 ("cxgb4: Adds CPL support for Shared Receive Queues")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>