Remove unnecessary computation of index (#6406)

Summary:
`index` can be replaced by  `iter`, saving the computation of `index++`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6406

Test Plan: make check

Differential Revision: D19905056

Pulled By: cheng-chang

fbshipit-source-id: add4638959c0d2e4e77a11f3fa04ffabaf0de790

table/multiget_context.h

@@ -94,8 +94,6 @@ class MultiGetContext {
       : num_keys_(num_keys),
         value_mask_(0),
         lookup_key_ptr_(reinterpret_cast<LookupKey*>(lookup_key_stack_buf)) {
-    int index = 0;
-
     if (num_keys > MAX_LOOKUP_KEYS_ON_STACK) {
       lookup_key_heap_buf.reset(new char[sizeof(LookupKey) * num_keys]);
       lookup_key_ptr_ = reinterpret_cast<LookupKey*>(
@@ -105,11 +103,10 @@ class MultiGetContext {
     for (size_t iter = 0; iter != num_keys_; ++iter) {
       // autovector may not be contiguous storage, so make a copy
       sorted_keys_[iter] = (*sorted_keys)[begin + iter];
-      sorted_keys_[iter]->lkey = new (&lookup_key_ptr_[index])
+      sorted_keys_[iter]->lkey = new (&lookup_key_ptr_[iter])
           LookupKey(*sorted_keys_[iter]->key, snapshot);
       sorted_keys_[iter]->ukey = sorted_keys_[iter]->lkey->user_key();
       sorted_keys_[iter]->ikey = sorted_keys_[iter]->lkey->internal_key();
-      index++;
     }
   }