pinctrl: qcom: spmi-mpp: Fix drive strength setting

It looks like we parse the drive strength setting here, but never
actually write it into the hardware to update it. Parse the setting and
then write it at the end of the pinconf setting function so that it
actually sticks in the hardware.

Fixes: 0e948042 ("pinctrl: qcom: spmi-mpp: Implement support for sink mode")
Cc: Doug Anderson <dianders@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>