aco: fix gfx10_wave64_bpermute

aco: fix gfx10_wave64_bpermute

Since 9254fb4fc72, the pass 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.

Although shuffles are disabled on GFX10, Detroit: Become Human seems to
use them anyway.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-By: Timur Kristóf <timur.kristof@gmail.com>
Fixes: 9254fb4fc72ed289ffded28ef067b4582973e90c ('aco: don't use a scalar
       temporary for reductions on GFX10')

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3683>