drm/msm: Add missing stub definition

DRM_MSM fails to build with DRM_MSM_DP=n; add the missing stub.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Fixes: 8ede2ecc ("drm/msm/dp: Add DP compliance tests on
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_drv.h

@@ -424,6 +424,11 @@ static inline int msm_dp_display_disable(struct msm_dp *dp,
 {
 	return -EINVAL;
 }
+static inline int msm_dp_display_pre_disable(struct msm_dp *dp,
+					struct drm_encoder *encoder)
+{
+	return -EINVAL;
+}
 static inline void msm_dp_display_mode_set(struct msm_dp *dp,
 				struct drm_encoder *encoder,
 				struct drm_display_mode *mode,