RDMA/ocrdma: Silence an integer underflow warning

We recently added a cap on "max_wqe_allocated" in 43a6b402


('RDMA/ocrdma: Create IRD queue fix').

My static checker complains that the cap has a problem because it
casts large values to negative.  "attrs->cap.max_send_wr" is a u32.
It comes from the user, but it's capped in ocrdma_check_qp_params() so
it can't wrap here.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>