drm/msm/dpu: Remove set but not used variable 'priv' in dpu_encoder_phys_vid.c

drm/msm/dpu: Remove set but not used variable 'priv' in dpu_encoder_phys_vid.c

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c: In function dpu_encoder_phys_vid_disable:
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c:566:26: warning: variable priv set but not used [-Wunused-but-set-variable]

It is not used since commit 25fdd5933e4c ("drm/msm:
Add SDM845 DPU support")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>