arm64: dts: mediatek: mt8390-genio-common: Fix pcie pinctrl dtbs_check error

Rename pcie pinctrl definition to fix the following dtbs_check error
for mt8370-genio-510-evk and mt8390-genio-700-evk devicetree files:
```
pinctrl@10005000: 'pcie-default' does not match any of the regexes:
  '-pins$', 'pinctrl-[0-9]+'
```

Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20250403-mt8390-genio-common-fix-pcie-dtbs-check-error-v1-1-70d11fc1482e@collabora.com


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>