RDMA/bnxt_re: Fix WQE Size posted to HW to prevent it from throwing error

Posting WQE size of 2 results in a WQE_FORMAT_ERROR
thrown by the HW as it requires host to supply WQE Size with room
for atleast one SGE so that the resulting WQE size be atleast 3.

Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>