IB/mlx4: Convert kmalloc to kmalloc_array for checkpatch

Convert kmalloc to be kmalloc_array to fix warnings below:

WARNING: Prefer kmalloc_array over kmalloc with multiply
+               qp->sq.wrid = kmalloc(qp->sq.wqe_cnt * sizeof(u64),

WARNING: Prefer kmalloc_array over kmalloc with multiply
+               qp->rq.wrid = kmalloc(qp->rq.wqe_cnt * sizeof(u64),

WARNING: Prefer kmalloc_array over kmalloc with multiply
+               srq->wrid = kmalloc(srq->msrq.max * sizeof(u64),

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>