net/mlx5: Lag, use local variable already defined to access E-Switch

Use the local variable for dev0 (and add from dev1) instead of using
the devices stored in the ldev structure. Makes the code easier
to read.

Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>