hwcomposer : Fixing copybit render buffer fence closing.

While closing the fence, correct index is not used.
Fixing the same.

Change-Id: I654ec4e649c247dca9c038e5b15184a01833bdc4
CRs-Fixed: 578408
diff --git a/libhwcomposer/hwc_copybit.cpp b/libhwcomposer/hwc_copybit.cpp
index 2104bff..8a6761f 100644
--- a/libhwcomposer/hwc_copybit.cpp
+++ b/libhwcomposer/hwc_copybit.cpp
@@ -296,9 +296,10 @@
         copybit_device_t *copybit = getCopyBitDevice();
         // Async mode
         copybit->flush_get_fence(copybit, fd);
-        if(mRelFd[0] >=0 && ctx->mMDP.version == qdutils::MDP_V3_0_4) {
-            close(mRelFd[0]);
-            mRelFd[0] = -1;
+        if(mRelFd[mCurRenderBufferIndex] >=0 &&
+           ctx->mMDP.version == qdutils::MDP_V3_0_4) {
+            close(mRelFd[mCurRenderBufferIndex]);
+            mRelFd[mCurRenderBufferIndex] = -1;
         }
     }
     return true;