Fix a comment in RateLimiter::RequestToken (#9933)

Summary:
**Context/Summary:**
- As titled

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9933

Test Plan: - No code change

Reviewed By: ajkr

Differential Revision: D36086544

Pulled By: hx235

fbshipit-source-id: 2bdd19f67e45df1e3af4121b0c1a5e866a57826d

util/rate_limiter.cc

@@ -31,8 +31,8 @@ size_t RateLimiter::RequestToken(size_t bytes, size_t alignment,
 
     if (alignment > 0) {
       // Here we may actually require more than burst and block
-      // but we can not write less than one page at a time on direct I/O
+      // as we can not write/read less than one page at a time on direct I/O
-      // thus we may want not to use ratelimiter
+      // thus we do not want to be strictly constrained by burst
       bytes = std::max(alignment, TruncateToPageBoundary(alignment, bytes));
     }
     Request(bytes, io_priority, stats, op_type);