Fix typo: rename "bounary" to "boundary" in block.cc (#7328)

Summary:
Fix typo in comment for SeekForGetImpl().
Rename "bounary" to "boundary"

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7328

Reviewed By: riversand963

Differential Revision: D23439748

Pulled By: zhichao-cao

fbshipit-source-id: 83a34c417c71a3210ce54a090d76c4d5571313f3

table/block_based/block.cc

@@ -291,7 +291,7 @@ bool DataBlockIter::SeekForGetImpl(const Slice& target) {
     // exist in the next block. Consider this example:
     //
     // Block N:    [aab@100, ... , app@120]
-    // bounary key: axy@50 (we make minimal assumption about a boundary key)
+    // boundary key: axy@50 (we make minimal assumption about a boundary key)
     // Block N+1:  [axy@10, ...   ]
     //
     // If seek_key = axy@60, the search will starts from Block N.