arm64: dts: qcom: apq8096-db820c: add PM8994 pin function

The bindings require that every pin configuration comes with 'function'
property.  Add such to PM8994 GPIO5.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220507194913.261121-8-krzysztof.kozlowski@linaro.org