soc: qcom: rpmh: Dirt can only make you dirtier, not cleaner

commit 35bb4b22

 upstream.

Adding an item into the cache should never be able to make the cache
cleaner.  Use "|=" rather than "=" to update the dirty flag.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Maulik Shah <mkshah@codeaurora.org> Thanks, Maulik
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Fixes: bb700067

 ("soc: qcom: rpmh: Update dirty flag only when data changes")
Reported-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200417141531.1.Ia4b74158497213eabad7c3d474c50bfccb3f342e@changeid
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>