drm/msm: dpu: Clean up _dpu_core_video_mode_intf_connected()

Local variable is not needed and condition can't be hit.

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>