Fix --oat-filename in dex2oat usage message

--oat-filename flag was moved to --oat-file, but an error message wasn't updated. This commit fixes the error message to the new --oat-file flag name.

Change-Id: I0cd0dcc00883975942ae92ef1f246bad5e5e8305
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 6950b93..acc206e 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -749,7 +749,7 @@
     }
 
     if ((output_vdex_fd_ == -1) != (oat_fd_ == -1)) {
-      Usage("VDEX and OAT output must be specified either with one --oat-filename "
+      Usage("VDEX and OAT output must be specified either with one --oat-file "
             "or with --oat-fd and --output-vdex-fd file descriptors");
     }