arm64: dts: fix regulator property name for wlan pcie endpoint

The property name vddpe-supply is not included in
Documentation/devicetree/bindings/pci/qcom,pcie.txt
nor in the pcie-qcom PCIe Root Complex driver.

This property name was used in an initial patchset for pcie-qcom,
but was renamed in a later revision.

Therefore, the regulator is currently never enabled, leaving us with
unoperational wlan.

Fix this by using the correct regulator property name, so that wlan
comes up correctly.

Fixes: 1c8ca74a2ea1 ("arm64: dts: apq8096-db820c: Enable wlan and bt en pins")
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>