arm64: dts: qcom: add correct drive strenght on cs pins

2mA drive strenght is not enough to drive chipselect low on hardware
configurations with level shifters, 16mA should give good range to
allow such configurations to work.

This issue was noticed while testing spi on db410c with sensor board.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>