RDMA/mlx5: Remove redundant allocation warning print

The kmalloc() failure to allocate memory generates enough information
and doesn't need to be accompanied by another driver print.

Fixes: d69a24e0

 ("IB/mlx5: Move IB event processing onto a workqueue")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>