aco: consider blocks unreachable if they are in the logical cfg

aco: consider blocks unreachable if they are in the logical cfg

unreachable was true if the last block is unreachable in the linear cfg,
but it should also be true if it is unreachable in the logical cfg.

Fixes dEQP-VK.graphicsfuzz.for-with-ifs-and-return

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Fixes: 8d8c864beba399ae4ee2267f680d1f600ad32767
    ('aco: improve check for unreachable loop continue blocks')

Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4764>