drivers: soc: qcom: rpmh: Correctly set dirty flag

Currently rpmh dirty flag is set for all cases regardless of
data is really updated or not. Correct it to update for
only those cases where data is updated.

Change-Id: I2c87ffbf1bae23ddd4b4cb7dced213cac267df59
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>