Fix IDE "PIO WRITE wait for ready" test under extreme interrupt load.

Fix IDE "PIO WRITE wait for ready" test under extreme interrupt load.

From Daniel Tram Lux: under extreme irq load on an underpowered CPU,
the timeout loop may not make any progress, and decide that a timeout
occurred before it has actually tested the status register.

The minimal fix for now is to just have a final test _after_ the timeout
to remove the problem. The real fix would likely be to not have irqs
enabled between reading the status and the timeout.