Fixed a flipped conditional when writing back the
values of variables in the Materializer.

The Materializer should not write the variable
back if its new value is the *same* as the old
value, not if the new value is *different*.

<rdar://problem/16712205>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207148 91177308-0d34-0410-b5e6-96231b3b80d8