aco: gfx10_wave64_bpermute fixes
Since 9254fb4f, setup_reduce_temp()
replaced the SCC clobber with the scalar
identity temporary. Just skip most of the temporary setup, since we don't
need it for gfx10_wave64_bpermute.
This isn't a real issue, since shuffles were disabled on GFX10 at that time (and still are).
Edited by Rhys Perry