drm: fixes crct set_mode when crtc mode_fixup is null.

This patch set nukes all the dummy crtc mode_fixup implementations.
(made on top of Daniel topic/drm-misc branch)

Signed-off-by: Carlos Palminha <palminha@synopsys.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/9d41105dee6632b4bb50e9555f2196ac249b9fce.1455630967.git.palminha@synopsys.com

drivers/gpu/drm/drm_crtc_helper.c

@@ -343,9 +343,12 @@ bool drm_crtc_helper_set_mode(struct drm_crtc *crtc,
 		}
 	}
 
-	if (!(ret = crtc_funcs->mode_fixup(crtc, mode, adjusted_mode))) {
-		DRM_DEBUG_KMS("CRTC fixup failed\n");
-		goto done;
+	if (crtc_funcs->mode_fixup) {
+		if (!(ret = crtc_funcs->mode_fixup(crtc, mode,
+						adjusted_mode))) {
+			DRM_DEBUG_KMS("CRTC fixup failed\n");
+			goto done;
+		}
 	}
 	DRM_DEBUG_KMS("[CRTC:%d:%s]\n", crtc->base.id, crtc->name);