nir/dead_cf: Call instructions aren't dead

When we inlined cf_node_has_side_effects into node_is_dead, all the
conditions flipped and we forgot to flip one.  Fortunately, it doesn't
matter right now because no one uses this pass on shaders with more than
one function.

Fixes: b50465d1 "nir/dead_cf: Inline cf_node_has_side_effects"
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
(cherry picked from commit 8948048c)