drm/msm/dpu: Correct the SA8775P intr_underrun/intr_underrun index

drm/msm/dpu: Correct the SA8775P intr_underrun/intr_underrun index

The intr_underrun and intr_vsync indices have been swapped, just simply
corrects them.

Cc: stable@vger.kernel.org
Fixes: b139c80d181c ("drm/msm/dpu: Add SA8775P support")
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/709209/
Link: https://lore.kernel.org/r/20260305-mdss_catalog-v5-2-06678ac39ac7@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>