This addresses an SMP-only issue with the EHCI driver, where only one CPU
should scan the schedule at a time (scanning is not re-entrant) but either
the IRQ handler or a watchdog timer could end up starting it.  Many thanks
to Olaf Hering for isolating the failure mode, and testing this fix!

Once once CPU starts scanning, any other might as well finish right
away.  This fix just adds a flag to detect that case.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>