ScalarEvolution: added tmp to avoid use-after-dtor in for loop.

Summary:
For loop destroyed current instance before invoking next.
Temporary variable added to prevent use-after-dtor when invoke
destructor on current instance.

Reviewers: eugenis

Subscribers: llvm-commits, sanjoy

Differential Revision: http://reviews.llvm.org/D12912

Rename temp var.

llvm-svn: 247867