drm/i915: convert pointless error checks in set_config to BUGs

Because they all are, the ioctl command never calls us with any of
these violated. Also drop a equally pointless empty debug message (and
also in set_cursor, while we're at it).

With all these changes, intel_crtc_set_config is neatly condensed down
to it's essence, the actual modeset code (or fb update calling code)

v2: The fb helper code is actually stretching ->set_config semantics a bit,
it calls it with set->mode == NULL but set->fb != NULL.
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -5462,8 +5462,6 @@ static int intel_crtc_cursor_set(struct drm_crtc *crtc,
 	uint32_t addr;
 	int ret;
 
-	DRM_DEBUG_KMS("\n");
-
 	/* if we want to turn off the cursor ignore width and height */
 	if (!handle) {
 		DRM_DEBUG_KMS("cursor off\n");
@@ -6920,16 +6918,9 @@ static int intel_crtc_set_config(struct drm_mode_set *set)
 	int ret;
 	int i;
 
-	DRM_DEBUG_KMS("\n");
-
-	if (!set)
-		return -EINVAL;
-
-	if (!set->crtc)
-		return -EINVAL;
-
-	if (!set->crtc->helper_private)
-		return -EINVAL;
+	BUG_ON(!set);
+	BUG_ON(!set->crtc);
+	BUG_ON(!set->crtc->helper_private);
 
 	if (!set->mode)
 		set->fb = NULL;