boards: st: stm32h745i_disco: m7: Fix PHY address

According to the datasheet, the PHY address is 0x1. When changed to this
value the PHY id is correctly read.

Before:
```
[00:00:00.602,000] <err> phy_mii: No PHY found at address 0
```

After:
```
[00:00:00.051,000] <inf> phy_mii: PHY (1) ID 7C111
```

Signed-off-by: Tomáš Juřena <jurenatomas@gmail.com>