drm/msm/dpu: always clear every individual pending flush mask

There are two tiers of pending flush control, top level and
individual hardware block. Currently only the top level of
flush mask is reset to 0 but the individual pending flush masks
of particular hardware blocks are left at their previous values,
eventually accumulating all possible bit values and typically
flushing more than necessary.
Reset all individual hardware block flush masks to 0 to avoid
accidentally flushing them.

Changes in V13:
-- rewording commit text
-- add an empty space line as suggested

Changes in V14:
-- add Fixes tag

Fixes: 73bfb790 ("msm:disp:dpu1: setup display datapath for SC7180 target")
Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/539508/
Link: https://lore.kernel.org/r/1685036458-22683-8-git-send-email-quic_khsieh@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>