drm/msm: avoid unused function warning

drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c:368:13: error: 'dpu_plane_danger_signal_ctrl' defined but not used [-Werror=unused-function]

Fixes: 7b2e7ade ("drm/msm/dpu: Make dpu_plane_danger_signal_ctrl void")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>