Just a pure method renaming.
It is a preparation step for replacing "memory space as raw integer"
with more generic "memory space as attribute", which will be done in
separate commit.
The MemRefType::getMemorySpace method will return Attribute and
become the main API, while getMemorySpaceAsInt will be declared as
deprecated and will be replaced in all in-tree dialects (also in separate
commits).
nit: I'd probably go with getMemorySpaceAsInteger, but I don't think it matters that much if it is going away soon.