drm_hwcomposer: fix new then free error for hwc_context_t

Change-Id: Id987b9eebe818ded689dbdfd1c695118b0a81d5e
diff --git a/hwcomposer.cpp b/hwcomposer.cpp
index 7a4b302..3d95415 100644
--- a/hwcomposer.cpp
+++ b/hwcomposer.cpp
@@ -1094,7 +1094,7 @@
 	if (ret)
 		ALOGE("Could not destroy import %d", ret);
 
-	free(ctx);
+	delete ctx;
 
 	return 0;
 }
@@ -1356,7 +1356,7 @@
 	if (ctx->fd >= 0)
 		close(ctx->fd);
 
-	free(ctx);
+	delete ctx;
 	return ret;
 }