[AArch64] Preserve chain when lowering fixed length load to SVE (PR55281)

When a fixed length load is lowered to an SVE masked load, the
result chain is currently set to the input chain of the old load,
rather than the result chain of the new load. This may cause stores
to be incorrectly reordered.

Fixes https://github.com/llvm/llvm-project/issues/55281.

Differential Revision: https://reviews.llvm.org/D125464