bnxt_re: Fix couple of memory leaks that could lead to IOMMU call traces

1. DMA-able memory allocated for Shadow QP was not being freed.
2. bnxt_qplib_alloc_qp_hdr_buf() had a bug wherein the SQ pointer was
   erroneously pointing to the RQ. But since the corresponding
   free_qp_hdr_buf() was correct, memory being free was less than what was
   allocated.

Fixes: 1ac5a404 ("RDMA/bnxt_re: Add bnxt_re RoCE driver")
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>