Eliminate the follow clang warning:

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:544:33: warning: variable
‘mode’ set but not used [-Wunused-but-set-variable].
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Fixes: 3177589c("drm/msm/dpu: encoder: drop unused mode_fixup callback")
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/487136/
Link: https://lore.kernel.org/r/20220524081413.37895-1-jiapeng.chong@linux.alibaba.comSigned-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>