drm/msm/dpu: Fix PP_BLK_DIPHER -> DITHER typo

SM8550 exclusively has a DITHER sub-block inside the PINGPONG block and
no other registers, hence the DITHER name of the macro and a
corresponding PINGPONG block length of zero.  However, the PP_BLK_ macro
name was typo'd to DIPHER rather than DITHER.

Fixes: efcd0107 ("drm/msm/dpu: add support for SM8550")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/534214/
Link: https://lore.kernel.org/r/20230411-dpu-intf-te-v4-5-27ce1a5ab5c6@somainline.org


Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>