drm/msm/dpu: correct MERGE_3D length

Each MERGE_3D block has just two registers. Correct the block length
accordingly.

Fixes: 4369c93c ("drm/msm/dpu: initial support for merge3D hardware block")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/542177/Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Link: https://lore.kernel.org/r/20230613001004.3426676-3-dmitry.baryshkov@linaro.org

drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c

@@ -508,7 +508,7 @@ static const struct dpu_pingpong_sub_blks sc7280_pp_sblk = {
 #define MERGE_3D_BLK(_name, _id, _base) \
 	{\
 	.name = _name, .id = _id, \
-	.base = _base, .len = 0x100, \
+	.base = _base, .len = 0x8, \
 	.features = MERGE_3D_SM8150_MASK, \
 	.sblk = NULL \
 	}