pinctrl: qcom: spmi-mpp: Set drive-strength for sink function

Write drive-strength setting into SINK_CTL register to make sink
function work.

Change-Id: I0b6e273b846a8e07c5b36d03a20edddfd895e9c0
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>