fix the crash bug when specifying non-existed option.

Change-Id: I68521b92c1c83bed81746d92fe11d50055843992

R=dhendrix@chromium.org
BUG=No bug id.
TEST=Tested with "vpd --clean", and program didn't segmentation fail.

Review URL: http://codereview.chromium.org/6728023
diff --git a/vpd.c b/vpd.c
index 11787ea..90aca89 100644
--- a/vpd.c
+++ b/vpd.c
@@ -565,6 +565,7 @@
     {"partition", 0, 0, 'i'},
     {"list", 0, 0, 'l'},
     {"overwrite", 0, 0, 'O'},
+    {0, 0, 0, 0}
   };
   char *filename = NULL;
   int write_back_to_flash = 0;