drm/fb-helper: Remove drm_mode_config_fb.

Remove drm_mode_config_fb, I don't see the point of it.
To make it clear that it's ok to use plane->fb directly,
move up drm_drv_uses_atomic_modeset so the code is skipped for atomic
drivers that require plane_state->fb.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170703115106.18783-1-maarten.lankhorst@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_fb_helper.c

@@ -298,20 +298,6 @@ int drm_fb_helper_debug_enter(struct fb_info *info)
 }
 EXPORT_SYMBOL(drm_fb_helper_debug_enter);
 
-/* Find the real fb for a given fb helper CRTC */
-static struct drm_framebuffer *drm_mode_config_fb(struct drm_crtc *crtc)
-{
-	struct drm_device *dev = crtc->dev;
-	struct drm_crtc *c;
-
-	drm_for_each_crtc(c, dev) {
-		if (crtc->base.id == c->base.id)
-			return c->primary->fb;
-	}
-
-	return NULL;
-}
-
 /**
  * drm_fb_helper_debug_leave - implementation for &fb_ops.fb_debug_leave
  * @info: fbdev registered by the helper
@@ -328,8 +314,11 @@ int drm_fb_helper_debug_leave(struct fb_info *info)
 		struct drm_mode_set *mode_set = &helper->crtc_info[i].mode_set;
 
 		crtc = mode_set->crtc;
+		if (drm_drv_uses_atomic_modeset(crtc->dev))
+			continue;
+
 		funcs = crtc->helper_private;
-		fb = drm_mode_config_fb(crtc);
+		fb = crtc->primary->fb;
 
 		if (!crtc->enabled)
 			continue;
@@ -342,9 +331,6 @@ int drm_fb_helper_debug_leave(struct fb_info *info)
 		if (funcs->mode_set_base_atomic == NULL)
 			continue;
 
-		if (drm_drv_uses_atomic_modeset(crtc->dev))
-			continue;
-
 		drm_fb_helper_restore_lut_atomic(mode_set->crtc);
 		funcs->mode_set_base_atomic(mode_set->crtc, fb, crtc->x,
 					    crtc->y, LEAVE_ATOMIC_MODE_SET);