Documentation: ACPI: DSD: fix block code comments

Use the '.. code-block:: none' to properly highlight the documented DSDT
entries. This also fixes warnings in the documentation build process.

Fixes: e71305ac ("Documentation: ACPI: DSD: Document MDIO PHY")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>