Remove redundant assignment in GrDrawTarget.cpp

BUG=skia:
R=bsalomon@google.com

Author: qiankun.miao@intel.com

Review URL: https://codereview.chromium.org/552273003
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index 3f1d1c8..af00ac8 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -818,7 +818,6 @@
     fTarget = target;
     bool success = true;
     if (fTarget) {
-        fTarget = target;
         success = target->reserveVertexAndIndexSpace(vertexCount,
                                                      indexCount,
                                                      &fVertices,