nir/opt_if: run opt_peel_loop_initial_if after all other optimizations

nir/opt_if: run opt_peel_loop_initial_if after all other optimizations

Fixes dEQP-VK.graphicsfuzz.loops-ifs-continues-call with RADV.

opt_if_loop_terminator can cause this optimization or
opt_if_simplification to be run on the non-SSA code.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Fixes: 52c8bc0130a ('nir: make opt_if_loop_terminator() less strict')
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2943
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4757>