Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:207: warning: Function parameter or member 'cur_slave' not described in 'dpu_encoder_virt'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:207: warning: Function parameter or member 'hw_pp' not described in 'dpu_encoder_virt'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:207: warning: Function parameter or member 'intfs_swapped' not described in 'dpu_encoder_virt'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1445: warning: Function parameter or member 'drm_enc' not described in '_dpu_encoder_trigger_flush'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1445: warning: Function parameter or member 'phys' not described in '_dpu_encoder_trigger_flush'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1445: warning: Function parameter or member 'extra_flush_bits' not described in '_dpu_encoder_trigger_flush'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1481: warning: Function parameter or member 'phys' not described in '_dpu_encoder_trigger_start'
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1564: warning: Function parameter or member 'dpu_enc' not described in '_dpu_encoder_kickoff_phys'

Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: freedreno@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>