mediatek: correct address of MT753x switch IC

mediatek: correct address of MT753x switch IC

For all boards currently working with the mt7530 DSA driver we can
be sure that the address of the switch on the MDIO bus is 31 --
simply because that address is hard-coded in the driver and the
address from the Device Tree is being ignore.

An upcoming patch will add support for MT753x ICs which are programmed
to addresses different from 0x1f using bootstrap pins. As a result the
address from the Device Tree will then be taken into account, which
will break currently working boards which got the address set to
anything else than 31.

While at it also unify the syntax in Device Tree to always us a decimal
value for the 'reg' property.

 * mt7622-buffalo-wsr-3200ax4s.dts
   Cosmetic change 'reg = <0x1f>' -> 'reg = <31>'

 * mt7622-dlink-eagle-pro-ai-ax3200-a1.dtsi
   Wrong address: 0 -> 31

 * mt7622-elecom-wrc-x3200gst3.dts
   Wrong address: 0 -> 31

 * mt7622-linksys-e8450.dtsi
   Wrong address: 0 -> 31

 * mt7622-ruijie-rg-ew3200.dtsi
   Wrong address: 0 -> 31

 * mt7622-xiaomi-redmi-router-ax6s.dts
   Wrong address: 0 -> 31

 * mt7629-iptime-a6004mx.dts
   Wrong address: 2 -> 31

 * mt7981b-zbtlink-zbt-z8102ax.dts
   Cosmetic change 'reg = <0x1f>' -> 'reg = <31>'

Signed-off-by: Daniel Golle <daniel@makrotopia.org>