Do not check JSON alignment of scalar accesses

When importing a schedule, do not verify the load/store alignment of
scalar accesses. Scalar loads/store are always created newly in code
generation with no alignment restrictions. Previously, scalar alignment
was checked if the access instruction happened to be a LoadInst or
StoreInst, but only its array (MK_Array) access is relevant.

This will be implicitly unit-tested when the access instruction of a
value read can be nullptr.

Differential Revision: http://reviews.llvm.org/D15680

llvm-svn: 257904