cxl: 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.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>