Fix wrong comment (Maximum supported block size)

Summary:
We can support SST files >2GB but we don't support blocks >2GB
Closes https://github.com/facebook/rocksdb/pull/1465

Differential Revision: D4132140

Pulled By: yiwu-arbug

fbshipit-source-id: 63bf12d

table/block.h

@@ -363,7 +363,7 @@ class BlockIter : public InternalIterator {
 
   // Return the offset in data_ just past the end of the current entry.
   inline uint32_t NextEntryOffset() const {
-    // NOTE: We don't support files bigger than 2GB
+    // NOTE: We don't support blocks bigger than 2GB
     return static_cast<uint32_t>((value_.data() + value_.size()) - data_);
   }