ScheduleDAGInstrs: Bug fix for missed memory dependency.

Summary:
In buildSchedGraph(), when adding memory dependencies for loads, move
the call to adjustChainDeps() after the call to
addChainDependency(AliasChain) to handle the case where
addChainDependency(AliasChain) ends up not adding a dependency and
instead putting the SU on the RejectMemNodes list.  The call to
adjustChainDeps() must be done after the call to addChainDependency() in
order to process the SU added to the RejectMemNodes list to create
memory dependencies for it.

Reviewers: hfinkel, atrick, jonpa, resistor

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D15927

llvm-svn: 256950