Add missing 'const' in aligned-atomic AO_XSIZE_load implementation

* src/atomic_ops/sysdeps/loadstore/aligned_atomic_load_store.template
(AO_XSIZE_load): Add missing 'const' (when casting away volatile).
* src/atomic_ops/sysdeps/loadstore/aligned_atomic_load_store.h:
Regenerate.
* src/atomic_ops/sysdeps/loadstore/int_aligned_atomic_load_store.h:
Likewise.
* src/atomic_ops/sysdeps/loadstore/short_aligned_atomic_load_store.h:
Likewise.