Update color type after color override in GrFillRectOp.

Fixes const_color_processor GM in MSAA mode after
https://skia.googlesource.com/skia/+/1d835423e1c6776c4cbdb91bd435d21a7c1e267c

Change-Id: I07cbe17d8986405da5211e106dca58bfd61e6bbd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201228
Auto-Submit: Brian Salomon <bsalomon@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>

src/gpu/ops/GrFillRectOp.cpp

@@ -150,6 +150,7 @@ public:
             for (int i = 0; i < this->quadCount(); ++i) {
                 fDeviceQuads.metadata(i).fColor = colorOverride;
             }
+            fColorType = GrQuadPerEdgeAA::MinColorType(colorOverride);
         }
 
         return result;