[Polly] Fix typo in comment. NFC.

[Meinersbur]

It's not a typo (which I understand as either a spelling error or grammatical error), more a correction of a not entirely accurate comment.

I will commit with a changed title.

Thanks for the contribution.

include/polly/ScopInfo.h

 
   SmallVector<Loop *, 4> NestLoops;
 
   std::string BaseName;
 
   /// The closest loop that contains this statement.
   Loop *SurroundingLoop;
 
-  /// Vector for Instructions in a BB.
+  /// Vector for Instructions in this statement.
   std::vector<Instruction *> Instructions;
 
   /// Build the statement.
   //@{
   void buildDomain();
 
   /// Fill NestLoops with loops surrounding this statement.
   void collectSurroundingLoops();

   /// Create a new SCoP statement for @p BB.
   ///
   /// A new statement for @p BB will be created and added to the statement
   /// vector
   /// and map.
   ///
   /// @param BB              The basic block we build the statement for.
   /// @param SurroundingLoop The loop the created statement is contained in.
-  /// @param Instructions    The instructions in the basic block.
+  /// @param Instructions    The instructions in the statement.
   void addScopStmt(BasicBlock *BB, Loop *SurroundingLoop,
                    std::vector<Instruction *> Instructions);
 
   /// Create a new SCoP statement for @p R.
   ///
   /// A new statement for @p R will be created and added to the statement vector
   /// and map.
   ///