net/mlx5e: Use proper name field for the UMR key

Even though some of the WQE control segment's field share
the same memory bits (a union of fields), prefer having the
right field name for every different usage.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>