[LoopVectorize] Use CreateAligned(Load|Store)

IRBuilder has CreateAligned(Load|Store) functions; use them and we don't need
to make a second call to setAlignment.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213453 91177308-0d34-0410-b5e6-96231b3b80d8