arm64: dts: qcom: sdm845-db845c: correct SPI2 pins drive strength

The pin configuration (done with generic pin controller helpers and
as expressed by bindings) requires children nodes with either:
1. "pins" property and the actual configuration,
2. another set of nodes with above point.

The qup_spi2_default pin configuration uses alreaady the second method
with a "pinmux" child, so configure drive-strength similarly in
"pinconf".  Otherwise the PIN drive strength would not be applied.

Fixes: 8d23a004 ("arm64: dts: qcom: db845c: add Low speed expansion i2c and spi nodes")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221010114417.29859-2-krzysztof.kozlowski@linaro.org