MIPS: Octeon: False positive timeout

If we reach the test just below the loop with a `timeout' value of 0,
this does not mean that the timeout caused the loop to end, but rather
the `smi_rd.s.pending', in the last iteration. If timeout caused the
loop to end, then `timeout' is -1, not 0.

Since this can occur only in the last iteration, it is not very likely
to be a problem. By changing the post- to prefix decrement we ensure
that a timeout of 0 does mean it timed out.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>