net/mlx5: remove Verbs query device duplication

net/mlx5: remove Verbs query device duplication

The sharing device context structure has a field named "device_attr"
which is filled by mlx5_os_get_dev_attr() function.
The spawn function calls mlx5_os_get_dev_attr() again and save it to
local variable identical to "device_attr" field.

There is no need for this duplication, because there is a reference to
the sharing device context structure from spawn function.

This patch removes the local "device_attr" from spawn function, and uses
the context's field instead.

Signed-off-by: Michael Baum <michaelba@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>