Since SCSISoftUSB relies on devices stalling (rather than doing a test unit ready), stalls occur when a card reader with no card present is queried.
The port of umass ends up trying to add something to the control transfer queue, but enters with interrupts disabled, so the clear endpoint stall just times out having not done anything (other callers have interrupts enabled so do clear the stall).
Apply change of policy that NetBSD made in revision 18.104.22.168 where the clear endpoint stall is cleared asynchronously rather than being left around until the next transfer is queued.
Since we don't have threads on RISC OS, and callbacks wouldn't happen either, we schedule a one shot RTSupport to trigger the clear at CBAI level.
Apply change from NetBSD 22.214.171.124 to remove the old clear code too.
Version 0.11. Tagged as 'XHCIDriver-0_11'