drm/msm/dpu: set DSC flush bit correctly at MDP CTL flush register

drm/msm/dpu: set DSC flush bit correctly at MDP CTL flush register

The CTL_FLUSH register should be programmed with the 22th bit
(DSC_IDX) to flush the DSC hardware blocks, not the literal value of
22 (which corresponds to flushing VIG1, VIG2 and RGB1 instead).

Changes in V12:
-- split this patch out of "separate DSC flush update out of interface"

Changes in V13:
-- rewording the commit text

Changes in V14:
-- drop 'DSC" from "The DSC CTL_FLUSH register" at commit text

Fixes: 77f6da90487c ("drm/msm/disp/dpu1: Add DSC support in hw_ctl")
Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/539496/
Link: https://lore.kernel.org/r/1685036458-22683-2-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>