Update GrPaint APIs to reflect lack of multiple color processors.

Change-Id: Ic7799b3c5f4294cba9ff72f8c11a2ad285ab189f
Bug: skia:10217
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/304738
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index c50bc6a..42d9d1a 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -345,7 +345,7 @@
     }
 
     if (paintFP) {
-        grPaint->addColorFragmentProcessor(std::move(paintFP));
+        grPaint->setColorFragmentProcessor(std::move(paintFP));
     }
 
     return true;