support 'cgpt repair'

src/platform/vboot_reference/utility/cgpt/cgpt_options.c

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Update GPT attribute bits.
  */
 #include <getopt.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include "cgpt.h"
@@ skipping 89 matching lines @@
     }
   }
   return CGPT_OK;
 }
 
 int OpenDriveInLastArgument(const int argc,
                             char *const *argv,
                             struct drive *drive) {
   /* Then, we need a non-option argument. */
   if (optind == (argc - 1)) {
-    char *drive_path;
-    drive_path = argv[optind];
+    char *path, drive_path[256];
+    path = argv[optind];
+    switch (path[0]) {
+      case '.':
+      case '/':
+        snprintf(drive_path, sizeof(drive_path), "%s", path);
+        break;
+      default:
+        snprintf(drive_path, sizeof(drive_path), "/dev/%s", path);
+        break;
+    }
     if (CGPT_OK != DriveOpen(drive_path, drive)) {
       printf("[ERROR] DriveOpen(%s) error!\n", drive_path);
       return CGPT_FAILED;
     }
   } else {
     printf("[ERROR] One (and only one) non-option argument is required.\n");
     return CGPT_FAILED;
   }
 
   return CGPT_OK;
 }