[sw, runtime] Fix `IBEX_SPIN_FOR`.
[sw, runtime] Fix `IBEX_SPIN_FOR`.

Signed-off-by: Douglas Reis <df95399f7253aef5711aa5e1f53e8824981313ab@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan