[Clang][AArch64] Fix 'svzero_za' intrinsic to take no arguments. (#82648)

We previously defined svzero_za as:

  void svzero_za();

rather than:

  void svzero_za(void);

Which meant that Clang accepted arguments. Compiling for example
`svzero_za(<non-constant integer>)` ended up with incorrect IR and a
compiler crash because it couldn't select an instruction for it.