Follow-up to r1717012, fix warning on incompatible pointer type

* config_store.c
  (cleanup_store): Make key a void pointer


git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1721792 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/config_store.c b/src/config_store.c
index 3180f07..e1fa215 100644
--- a/src/config_store.c
+++ b/src/config_store.c
@@ -141,7 +141,7 @@
          hi;
          hi = apr_hash_next(hi))
       {
-          const char *key;
+          const void *key;
           void *val;
 
           apr_hash_this(hi, &key, NULL, &val);
@@ -155,7 +155,7 @@
          hi;
          hi = apr_hash_next(hi))
       {
-          const char *key;
+          const void *key;
           void *val;
 
           apr_hash_this(hi, &key, NULL, &val);