Cleanup: Go with SkDebugf instead of GrPrintf.

Since GrPrintf is just defined to SkDebugf, we can go with the later
directly.

BUG=None
TEST=None
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/695663003
diff --git a/src/gpu/GrDrawState.h b/src/gpu/GrDrawState.h
index 036c4a5..39c9102 100644
--- a/src/gpu/GrDrawState.h
+++ b/src/gpu/GrDrawState.h
@@ -419,10 +419,10 @@
         }
     #ifdef SK_DEBUG
         if (GrBlendCoeffRefsDst(dstCoeff)) {
-            GrPrintf("Unexpected dst blend coeff. Won't work correctly with coverage stages.\n");
+            SkDebugf("Unexpected dst blend coeff. Won't work correctly with coverage stages.\n");
         }
         if (GrBlendCoeffRefsSrc(srcCoeff)) {
-            GrPrintf("Unexpected src blend coeff. Won't work correctly with coverage stages.\n");
+            SkDebugf("Unexpected src blend coeff. Won't work correctly with coverage stages.\n");
         }
     #endif
     }