[VectorCombine] Fix for non-zero addrspace when creating vector load from scalar load

This is a fixup to commit 43bdac29, to make sure the
address space from the original load pointer is retained in the
vector pointer.

Resolves problem with
  Assertion `castIsValid(op, S, Ty) && "Invalid cast!"' failed.
due to address space mismatch.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D85912