[NFC] Fix an incorrect comment about operator precedence. (#105784)

The comment talks about left-associative operators twice, when the
latter mention is actually describing right-associative operators.

Author: mpark

clang/lib/Parse/ParseExpr.cpp

@@ -607,7 +607,7 @@ Parser::ParseRHSOfBinaryExpression(ExprResult LHS, prec::Level MinPrec) {
         RHS = ExprError();
       }
       // If this is left-associative, only parse things on the RHS that bind
-      // more tightly than the current operator.  If it is left-associative, it
+      // more tightly than the current operator.  If it is right-associative, it
       // is okay, to bind exactly as tightly.  For example, compile A=B=C=D as
       // A=(B=(C=D)), where each paren is a level of recursion here.
       // The function takes ownership of the RHS.