drm/msm/dp/dp_display: Remove unused variable 'hpd'

drm/msm/dp/dp_display: Remove unused variable 'hpd'

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

 drivers/gpu/drm/msm/dp/dp_display.c: In function ‘dp_display_usbpd_attention_cb’:
 drivers/gpu/drm/msm/dp/dp_display.c:496:19: warning: variable ‘hpd’ set but not used [-Wunused-but-set-variable]

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: Kuogee Hsieh <khsieh@codeaurora.org>
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>
Link: https://lore.kernel.org/r/20210303134319.3160762-4-lee.jones@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>