Fix oatdump's usage message.

Change-Id: I3d0e1797984ea0ee7c7a4303e959e54a6066809a
diff --git a/src/oatdump.cc b/src/oatdump.cc
index b4ba3df..866c180 100644
--- a/src/oatdump.cc
+++ b/src/oatdump.cc
@@ -48,7 +48,7 @@
           "\n");
   fprintf(stderr,
           "  --oat-file=<file.oat>: specifies an input oat filename.\n"
-          "      Example: --image=/system/framework/boot.oat\n"
+          "      Example: --oat-file=/system/framework/boot.oat\n"
           "\n");
   fprintf(stderr,
           "  --image=<file.art>: specifies an input image filename.\n"