RDMA/mlx4: Remove NULL check before dev_{put, hold}

The call netdev_{put, hold} of dev_{put, hold} will check NULL,
so there is no need to check before using dev_{put, hold}.

Fix the following coccicheck warnings:
/drivers/infiniband/hw/mlx4/main.c:1311:2-10: WARNING:
WARNING  NULL check before dev_{put, hold} functions is not needed.

/drivers/infiniband/hw/mlx4/main.c:148:2-10: WARNING:
WARNING  NULL check before dev_{put, hold} functions is not needed.

/drivers/infiniband/hw/mlx4/main.c:1959:3-11: WARNING:
WARNING  NULL check before dev_{put, hold} functions is not needed.

/drivers/infiniband/hw/mlx4/main.c:1962:3-10: WARNING:
WARNING  NULL check before dev_{put, hold} functions is not needed.

Signed-off-by: zhang songyi <zhang.songyi@zte.com.cn>
Link: https://lore.kernel.org/r/202211291554079687539@zte.com.cn


Signed-off-by: Leon Romanovsky <leon@kernel.org>