devlink: Remove eswitch mode check for mode set call

When eswitch is disabled, querying its current mode results in error.
Due to this when trying to set the eswitch mode for mlx5 devices, it
fails to set the eswitch switchdev mode.
Hence remove such check.

Fixes: a8ecb93e ("devlink: Introduce rate nodes")
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>