c_rehash: fix hash_name output for small hashes

The hash lookup is done by 8-character hash.

Author: orgads

sample/c_rehash.rb

@@ -156,7 +156,7 @@ def path(filename)
   end
 
   def hash_name(name)
-    sprintf("%x", name.hash)
+    sprintf("%08x", name.hash)
   end
 
   def fingerprint(der)