fix compilation error in GrContext.cpp when PREFER_MSAA_OFFSCREEN_AA is enabled

http://codereview.appspot.com/5534068/



git-svn-id: http://skia.googlecode.com/svn/trunk@3009 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index a406629..d4264d5 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -809,7 +809,7 @@
     GrDrawState* drawState = target->drawState();
     drawState->setRenderTarget(offRT0);
 #if PREFER_MSAA_OFFSCREEN_AA
-    target->enableState(GrDrawState::kHWAntialias_StateBit);
+    drawState->enableState(GrDrawState::kHWAntialias_StateBit);
 #endif
 
     GrMatrix transM;