net: fsl: Use device_type helpers to access the node type

Remove directly accessing device_node.type pointer and use the accessors
instead. This will eventually allow removing the type pointer.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>