arm64: dts: qcom: sa8775p-ride: index the first SGMII PHY

arm64: dts: qcom: sa8775p-ride: index the first SGMII PHY

We'll be adding a second SGMII PHY on the same MDIO bus, so let's index
the first one for better readability.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Tested-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20230810080909.6259-6-brgl@bgdev.pl
Signed-off-by: Bjorn Andersson <andersson@kernel.org>