arm64: dts: rockchip: set PHY address of MT7531 switch to 0x1f

[ Upstream commit a2ac2a1b

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The MT7531 switch listens on PHY address 0x1f on an MDIO bus. I've got two
findings that support this. There's no bootstrapping option to change the
PHY address of the switch. The Linux driver hardcodes 0x1f as the PHY
address of the switch. So the reg property on the device tree is currently
ignored by the Linux driver.

Therefore, describe the correct PHY address on Banana Pi BPI-R2 Pro that
has this switch.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Fixes: c1804463 ("arm64: dts: rockchip: Add mt7531 dsa node to BPI-R2-Pro board")
Link: https://lore.kernel.org/r/20240314-for-rockchip-mt7531-phy-address-v1-1-743b5873358f@arinc9.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>