RDMA/mad: Allocate zeroed MAD buffer

Ensure that MAD output buffer is zero-based allocated in all the callers
of process_mad and remove the various memset()'s from the drivers.

Link: https://lore.kernel.org/r/20191029062745.7932-3-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/ocrdma/ocrdma_stats.c

@@ -675,7 +675,6 @@ int ocrdma_pma_counters(struct ocrdma_dev *dev,
 {
 	struct ib_pma_portcounters *pma_cnt;
 
-	memset(out_mad->data, 0, sizeof out_mad->data);
 	pma_cnt = (void *)(out_mad->data + 40);
 	ocrdma_update_stats(dev);